chem geek

So let me get this straight. You drained and refilled your hot tub and then used Dichlor for only 2 weeks. Then you measured the CYA levels and they were over 100. Is that right? That doesn't make sense unless you were using way too much Dichlor. To get to a CYA level of over 100 you would have had to have added over 100 ppm FC equivalent of chlorine over the two weeks. That's about 7 ppm FC every day. That is possible (especially if you also used Dichlor to "shock" once or twice), but it's more chlorine than you would have needed -- did you check Free Chlorine (FC) levels each time or did you just add some Dichlor? If you just added Dichlor each night, how did you figure out how much to add? How much did you add and how many gallons are in your hot tub? As for how to lower CYA, it can only be lowered by a partial drain and refill -- you'd have to dilute about 4/5ths of the water in your hot tub to get it down to a reasonable level (assuming it's at about 100 ppm right now). The next time you do a full drain and refill, just use Dichlor for just a few days, not 2 weeks, and only add enough for about 4 ppm FC each time. If you let me know your hot tub size, I can tell you how much you should probably be adding, but a good chlorine test kit will give you a better idea. A tablespoon of Dichlor in 500 gallons of water would give 4.15 ppm FC and 3.8 ppm CYA so perhaps your spa is smaller than 500 gallons in which case your FC and CYA increases each night were more. If your spa was 300 gallons, then the FC would increase by 6.9 ppm while the CYA would increase by 6.3 ppm which sounds more like what happened. If you added Dichlor for shocking, then that would account for a large increase as well. Don't worry about taking a while to get used to all of this. It only sounds complicated initially, but once you get the hang of it then it really is quite easy.

Yes, you stick to bleach, even for shocking. If you have an accurate drop-based FAS-DPD chlorine test kit, such as found in the Taylor K-2006 (or the K-1515-A if you only want the chlorine part of the test), then you can accurately measure Free Chlorine (FC) and Combined Chlorine (CC). You should see if you can keep the CC at less than 0.5 ppm (so 2-3 drops in the test if measuring using the 25ml sample for 0.2 ppm accuracy). If you find that bleach alone is not letting you keep the CC low, then you can use a non-chlorine shock (postassium monopersulfate - KMPS) instead and this would be done using a weekly maintenance dose. Howver, non-chlorine shock is more expensive so see if the chlorine (bleach) works for you and let us know how it works out. Once you've initially added CYA to your spa by using Dichlor a few times, you don't want to go back to it until you change your water of if you had significant splash-out and refill (not evaporation and refill as that does not remove the CYA). You could test your CYA after a month or so just to see that there is some in there -- enough to make the test a little cloudy, but not enough to not see the black dot (since that is probably 30 ppm in your test kit). I suspect you will find that the CYA does not go away, but if it did, you could just use Dichlor again a few times.

Yes, you should switch to bleach. And yes, it's fine to use unscented bleach that is less than 5%. You just don't get much for your money, but for a spa you don't use that much anyway. I'm surprised you can't find Clorox Regular (unscented) since that is 6%, but it really doesn't matter. If the total amount of Dichlor you added through the week, including the shock amount, adds up to adding the equivalent of about 20 ppm FC, then you have the right amount of CYA in your spa (it'll be about 18 ppm CYA since every 1 ppm FC from Dichlor also adds 0.9 ppm CYA) and should try and maintain 4 ppm FC. That will be enough to kill the bacteria that causes "hot tub itch" which is the hardest thing to kill in a spa.

waterbear's advice is, of course, right on the money. The thing is, that if the CYA level is really still over 100 (which could be true if you started with 800 then with dilution this would be 400, 200, 100), then the amount of Free Chlorine you would need to kill algae would be really, really high at about 40 ppm FC. At 30-40 ppm CYA, killing algae needs 15-20 ppm FC. Why don't you try waterbear's advice of maintaining 25 ppm FC and see what happens and let us know. After this is all over and you've gotten things under control, you should not use any chlorine sources that contain CYA, such as Trichlor tablets or Dichlor powder. Just use chlorinating liquid or unscented bleach as your sole source of chlorine (at least until next season when you might need to add more CYA by using Trichlor for a while or adding CYA directly).

Did you do your drain and refill in two steps -- drain half, then refill? Or did you do it with a continuous drain in one part of the pool will filling in another part and just keeping track of how much water? If I assume the former, then your CYA would go from 300 to 150 to 75 to 38 and that is consistent with your test strip reading. I am not aware of what would cause interference in the Taylor CYA test which just adds melamine (which combines with CYA to form melamine cyanurate which is minimally soluable and therefore produces a cloudy precipitate). If the pool water is not near room temperature, then you can get a false reading, but it will be too low because either the water is too cold so that the precipitate takes too long to form or it will be too hot so that the precipitate is more soluble. Nevertheless, I would say that having your chlorine used up so quickly overnight means that there is something in your pool consuming lots of chlorine. It could be nascent algae or lots of organics or ammonia/urea. You should continue to shock with bleach and try and keep the FC level up by adding chlorine several times if you can (at least twice per day -- morning and night). Eventually, you will breakdown or kill whatever it is that is consuming the chlorine and the chlorine should hold its level overnight (not during the day, however, if it's exposed to sunlight -- even with CYA it can get cut down by half in a full day of strong sun). You might also check and clean your filter if it looks like its trapped a bunch of junk (dead algae, organics, etc.) as the chlorine will also get used up trying to breakdown whatever is stuck in the filter, not just what is in your pool water. After your chlorine holds, try retesting your CYA level with your Taylor test kit. Let us know the results. If the measurement is now around 30-40 ppm, then whatever it was you killed or oxidized with the chlorine must have interfered with the Taylor CYA test. That would be good to know about.

The stabilizer level (Cyanuric Acid or CYA) is way, way too high. The disinfecting and oxidizing power of chlorine is roughly proportional to the ratio of Free Chlorine (FC) to the CYA level so with the high stabilizer (CYA) level you have, the chlorine is much less effective. In a spa, there is a somewhat hard to kill bacteria that causes "hot tub itch" so that in spas using chlorine without other systems (ozonator or Nature 2) you would want no more than 20 ppm CYA and have a minimum of 4 ppm FC. In theory with the ozonator and with Nature 2, you can use a lower amount of chlorine, but the high stabilizer level is making the chlorine you could have much less effective. You should be aware that for every 1 ppm FC that Dichlor adds to your spa, it also adds 0.9 ppm of stabilizer (CYA). So with your high stabilizer, you should just be adding unscented bleach to get your FC level to around 4 ppm since that would be equivalent to having an FC level of 0.8 ppm or less if you only had the 20 ppm CYA you should have. The next time you drain and refill your spa, just use Dichlor 4-5 times and then switch to using unscented bleach (until the next time you drain and refill in a few months, then start over with Dichlor 4-5 times, etc.). With a 20 or so ppm CYA (which a test kit can barely test so just go on the basis of using enough Dichlor to add about 20 ppm FC cumulatively, obviously not all at once), then after you switch to bleach you can just keep about 1 ppm FC in your spa (you'll need to start with more, maybe 2 ppm, and see if it ends up at 1 ppm the next time you use the spa and before you add more chlorine) and you should be fine since the ozonator and copper/silver from Nature2 should disinfect and prevent algae. Of course, you have another alternative and that would be to just drop the Nature2 completely since it's expensive and you really don't need it since you've already got an Ozonator and are using chlorine. Up to you. By the way, as for adding MetalX due to tea staining from your fill water, you should understand that Nature2 does nothing more than add copper and silver to your water -- i.e. metals! So adding MetalX may be incompatible with using Nature2 and perhaps it was the Nature2 that was giving you copper staining in the first place. Copper ions tend to inhibit algae while silver ions tend to kill some bacteria (neither kills viruses or protozoa, but the Ozonator should). In my opinion, Nature2 is an expensive waste, especially since you already have an ozonator and that alone should allow you to use somewhat lower chlorine levels. You have to have some disinfectant in the body of your spa water, but chlorine alone (with some conditioner - CYA) is sufficient.

Yes, if you add bromine to your pool by adding sodium bromide and then adding either chlorine or non-chlorine shock (KMPS) to activate it (i.e. to convert the bromide to bromine), then you can replace your floater. However, you will need to stay on top of your bromine level and keep it at 10 ppm (you should have a bromine test kit). You will need to regularly (probably daily or every other day) add chlorine and/or shock to reactivate the bromide back to bromine and occassionally you may need to add more sodium bromide (but probably not very often as bromide/bromine tends to stay in the spa rather well -- unlike chlorine that tends to leave quickly). The floater is more convenient as it continually introduces more "already activated" bromine into your spa, but it's really up to you as to which method you prefer. Another sanitation option is to just use chlorine alone. This would make sense if you had any irritation or sensitivity to bromine (some people do). To use chlorine alone, you would start (after a fresh drain and refill of the spa) by using Dichlor about 3-4 times (assuming each addition was equivalent to 4 ppm of chlorine) and then you would switch to using unscented bleach thereafter (until the next drain and refill in a few months). You've got alternatives -- the choice is up to you.

waterbear (Evan) can probably answer this better than I can since I sometimes get this mixed up, but I believe the Brom-a-guard tablet you have is essentially a combined system that contains both the bromine and the chlorine in the same initial chemical. In other words, it is already equivalent to starting with sodium bromide and then adding chlorine or non-chlorine shock to activate it (and, I believe, having extra chlorine as well since I believe you will have both bromine and chlorine initially). The shock you are using is indeed the same as potassium monopersulfate (KMPS) as peroxymonosulfate is just a synonym for monopersulfate. The reason for the claim that it is 100% pure and yet only has 42.8% potassium preoxymonsulfate is that this compound is part of a larger compound that has potassium sulfate and potassium bisulfate in it (the compound is K2SO4•KHSO4•2KHSO5). The only truly "active" part of this compound is the extra oxygen found in that last part and is given up as SO5 converts to SO4 -- oxygen gets reduced (and takes away electrons from) other compounds that get oxidized. The rest of this compound mostly just adds potassium and sulfates to your water (and lowers the ph by adding hydrogen ions). In your spa, the bromine will disinfect (kill bacteria and viruses) and prevent algae growth forming bromide while the chlorine will do the same and will reactivate the bromide to bromine and may also oxidize some compounds. When you add the shock, this will reactivate the bromide back to bromine. The shock will also oxidize organics. The Brom-a-Guard is acidic and the non-chlorine shock is very acidic so you will probably have to keep your TA up high enough to compensate (aeration from your spa jets will help make the pH rise to compensate the acidity of the products you add). If your pH still drops, then you'll need to add pH Up (sodium carbonate) to raise it. So, bottom line, is that you already have what you need and do not need to get or add sodium bromide.

Mike, It's funny you should mention "shocking" because I was just going to write another post to you about that. I can give you a very good idea of the situation in outdoor pools exposed to sunlight, but for spas I don't have enough information to be sure, so I'll describe what I know and don't know below for each situation. 1) In an outdoor pool exposed to sunlight, regular doses of chlorine that maintain sufficiently high chlorine levels at all times seem to continually achieve "breakpoint" and break down any combined chlorine that forms. Sometimes after heavier bather load, the combined chlorine (CC) rises a bit, but it usually goes back down over a day though some users just super-chlorinate (see point 2 below). 2) If you shock with chlorine (bleach), then you need to raise the Free Chlorine (FC) level to 10 times the Combined Chlorine (CC) level. However, though this tends to work OK at breaking down ammonia/urea based chloramines, it does not tend to break down other chlorinated organic compounds very well. 3) Non-chlorine shock such as Potassium Monopersulfate (KMPS or MPS) is best used as a regular maintenance dose (i.e. weekly) so that it is always present in the water at some level. The reason is that KMPS will oxidize both ammonia/urea (and/or monochloramine) and organics before chlorine gets a chance to so essentially you never build up any Combined Chlorine (CC). KMPS does not do as well breaking down already pre-existing Combined Chlorine (CC) including chlorinated organics, so that is why it is better to use it as maintenance rather than as a substitute for superchlorination. As for how much MPS to use in your spa, you'll have to do the math to convert the "maintenance" dosage requirement for your volume of water. There is some speculation that perhaps exposure to sunlight helps break down some Combined Chlorine (CC). That would explain situation (1) above where no additional shocking seems to be needed for most outdoor pools that are well maintained with chlorine alone. Indoor pools seem to have more problems with Combined Chlorine and I suspect spas might as well, but I really don't know. So here's what you can do. If you just want to skip right to playing it safe and easy, then use a small weekly dose of KMPS non-chlorine shock. This will prevent Combined Chlorine from forming in the first place so your friend is incorrect that you should alternate with super-chlorination. Only if for some reason you didn't use enough KMPS or forgot to use it and then had CC form, then it might make sense to super-chlorinate (once). Now, if you want to help solve a mystery for others, and be known in the halls of science as a great contributor to knowledge about spas (am I kissing up enough?), then you could get yourself an accurate FAS-DPD chlorine test kit such as the Taylor K-1515-A (or for additional testing including pH, TA, CYA, CH you can get the Taylor K-2006). Then, before using any KMPS in your spa, try measuring both the FC and CC levels over time (measure these BEFORE you get in to use the spa). See if the CC builds up or if simply maintaining the FC level is enough to keep CC below 0.5 ppm at all times (in my pool, it never gets above one drop in the test which is 0.2 ppm). The reason I say to do this experiment before you start using KMPS is that KMPS interferes with the CC test and in fact gets reported as CC itself. Taylor makes a reagent that removes this inteference, allowing you to measure CC and KMPS separately, but this is expensive (the Taylor K-1520 special reagent to remove monopersulfate interference is $19). And for being such a good sport and in the hope of learning more about spas, I'll sign this post with my real (first) name. Richard P.S. If you do end up using MPS on a regular basis, then remember that this is acidic so your pH might tend to go down. If that happens, you can increase your TA level to try and balance the tendency of the pH to go up with carbon dioxide outgassing vs. the tendency to go down from MPS. If you use a typical pH Up product that is Sodium Carbonate, then you will increase both pH and TA simultaneously which might be better to do at first if your pH drops measureably from the MPS. As for downsides to superchlorination and MPS, superchlorination will raise the FC level so that you will need to wait for it to drop before using your spa again. Superchlorination also adds more chlorine to your spa and that largely gets converted to salt (generally not a problem). MPS is acidic so TA needs to be higher to compensate (mentioned above) and its by-product is potassium sulfate. High sulfate levels may hurt certain kinds of surfaces -- I don't remember exactly which, though I believe it might be fiberglass, but you probably would have to add a heck of a lot of MPS before it becomes a problem, especially since you change your water completely every few months. One advantage unique to MPS is that by oxidizing ammonia/urea (and/or oxidizing monochloramine) and organics before chlorine gets a chance to, this tends to eliminate any odor problems from chloramines and virtually eliminates disinfection by-products (DPBs) including carcinogenic compounds. However, by your using CYA in your spa (from the initial few Dichlor additions) you already have lower chlorine levels (by a factor of 10-20) that reduce the rate of DPB production compared to indoor pools with no CYA where reports of asthma and other respiratory problems are found in competitive swimmers and small children.

Mike, Your most welcome. Be sure and keep us posted if anything changes or you have any other queestions. With only a little dichlor initially, you're probably good at the lower 2-3 ppm FC you end up with when you go into your spa. If you had used more dichlor (4-5 times instead of 2 times), then you may have needed 4 ppm FC minimum. Since the chlorine seems to be holding, you've got enough CYA in your spa from the dichlor. As you figured out, it's a delicate balance and a learning curve for your particular spa. In the past, you were fighting low pH because 1) MPS is acidic and 2) Dichlor is acidic when the chlorine gets used up (Dichlor is only slightly acidic initially, but the using up of chlorine is acidic). Now that you are using bleach, the pH from this chlorine addition (which is basic/alkaline) and usage (which is acidic) is pretty much neutral. So other factors, such as carbon dioxide outgassing, become the ones that determine where the pH goes and that means it will tend to rise. That's why the lower TA helps since it reduces the tendency to rise by having less of that carbon dioxide (carbonate) in your spa. Now it's time to open a cold one, get into that spa, and just enjoy! And say goodbye to "hot tub itch"!

Mike, I forgot to respond to your question about white vinegar. It is true that this is acetic acid so would lower the pH, but this isn't the typical acid used in pools or spas and is an organic compound that might consume some chlorine, so I wouldn't use that as your acid source. As I said in the previous post, keeping your TA LOWER will actually help prevent the rise in pH you normally see. Yes, it's counterintuitive, but it works. One more thing about the chlorine going away. Do you keep your spa covered when not in use? Did you use the spa or have the jets running at any time between your chlorine addition and the next time you measured the chlorine? Having the spa uncovered and especially running the jets will release chlorine into the air and deplete it from the spa. The rate at which this occurs is a function of the actual disinfecting chlorine amount in the spa so without CYA about half of the Free Chlorine amount is in the disinfecting form that can outgas, so this happens rapidly (with increased temperature and aeration, as found in a spa) and all of the chlorine can go away quickly (the non-disinfecting form of chlorine converts to the disinfecting form rapidly as it is used up). By using Dichlor initially, you add CYA to the spa and this significantly reduces the disinfecting chlorine concentration (by a factor of 10 or more, after a few Dichlor uses) and that reduces the amount of loss through outgassing. The key is to use enough CYA, but not too much -- i.e. slow down the chlorine outgassing, but still have enough to kill the bacteria that causes "hot tub itch".

Mike, Don't add any more baking soda. You want your TA to be around 70 ppm or else you will be fighting rising pH and having to add more acid. Higher TA (even 110) combined with the aeration of your spa jets causes the pH to rise by outgassing carbon dioxide. So ironically even though TA buffers pH, too much TA forces it to rise (especially with aeration). So keep the TA at 70 ppm (approximately, since it's darn hard to get anything exact in a spa). As for the CYA, though there may be some left, if you don't even see cloudiness in the test then you could probably use Dichlor at least two times. If the water in the CYA test turns cloudy, even if the black dot does not disappear, then you're probably at the right level. You can, of course, just see how it goes, but without enough CYA the chlorine will tend to dissipate quickly (which is what you are currently seeing) and it will have some "clean" smell and will degrade your swimsuits faster. In other words, use Dichlor the first few times since that will 1) keep the chlorine from leaving the spa so quickly and 2) will make the spa smell less like chlorine and 3) will lower the chlorine concentration so that it won't be "too much" for your swimsuits. I think your problem with bleach chlorine going away quickly will get resolved if you use Dichlor the first few times. Try this and keep us posted.

Mike, I can calculcate what you need and refer you to the spreadsheet I use at this link, but I designed this for pools (so you need to convert fluid ounces to tablespoons and teaspoons) and for understanding pool water chemistry and is NOT for novice users (my spreadsheet indicates that Ultra is 8% so don't go by the names, but by the 6% which I call Regular). Nevertheless, it is what I use to give you the numbers below. Starting with a fresh water refill, you first need to add some Baking Soda (Sodium Bicarbonate) which is also sold more expensively in pool/spa stores as Alkalinity Up or some similar name. You don't want to get your Total Alkalinity (TA) level too high or else you will fight pH rise due to the outgassing of carbon dioxide (adding bicarbonate to your pool is like carbonating a beverage). The TA will help reduce swings in pH. You need to add 5.5 ounces (weight) which is probably about 2.4 fluid ounces or about 5 tablespoons to get to 70 ppm TA IF you started with 0 ppm TA in your fill water (which is unlikely), so test your fill water and scale down the amounts I gave proportionately. Check with your spa heater's recommendation as to whether it requires the addition of calcium in addition to the carbonate. If the heater uses copper in its heat exchanger, then it might require the calcium carbonate to be closer to saturation. If the heater uses a corrosion resistant alloy, such as cupro-nickel, then it may not need any additional Calcium Hardness (CH). If Calcium were needed, then you would need to add about 7.2 ounces (weight) of anhydrous calcium chloride which is about 3.2 fluid ounces (6 and a half tablespoons) or 8.4 oucnes (weight) of calcium chloride dihydrate which is about 9.6 fluid ounces (19 tablespoons) to get to 150 ppm CH which is below saturation so that the heater (assuming 30F hotter at the heat exchanger surface) will be near saturation. These amounts assume you start with 0 ppm CH (which is unlikely), so test your fill water and scale down the amounts I gave proportionately. Your pH at this point will likely be about 8.3 (without adding calcium) or 7.9 (with adding calcium) since the Baking Soda will tend to push toward that pH. If you are at a pH of 8.3, then you next need to add 0.6 ounces (weight) of Sodium Bisulfate dry acid. That is probably about 0.25 fluid ounces or about half a tablespoon or one-and-a-half teaspoons. If you are at a pH of 7.9, then you add about 0.3 ounces (weight) of Sodium Bisulfate dry acid that is probably about 0.11 fluid ounces or a little more than half a teaspoon. This will get you down to a pH of around 7.5. Obviously, this part of adding acid is tricky so adding a little, mixing, and retesting is the best approach (true for other chemical additions as well -- add less than expected then see where you are at). Next comes adding chlorine. To minimize "fresh" chlorine smell from the outgassing of chlorine and to minimize the degradation and fading of your swimsuits as well as minimizing disinfection by-products, you want to initially use Dichlor a few times to build up a LOW amount of CYA, to no more than 20 ppm. To get to an absolute minimum of 4 ppm Free Chlorine (FC), you need to add 0.3 ounces (weight) of Dichlor. It looks like the density of Dichlor is about 1 ounce (weight) to 1 fluid ounce which seems light to me as this is similar to water. Anyway, if that's true, then you would add about 0.3 fluid ounces which is a little less than 2 teaspoons (2 teaspoons is fine). Just remember, that for every 1 ppm of FC that you add, you also add 0.9 ppm of Cyanuric Acid (CYA). Also, the 4 ppm FC should be the absolute minimum you should have, so if your spa loses that amount over the period of time between chlorine additions, then you need to start with 8 ppm FC so that it becomes 4 ppm FC the next time you add chlorine. You said that 1 tablespoon (which is 3 teaspoons) resulted in 3-5 ppm FC (or "maintained" that, but I'm not sure how much FC increase that means) so you'll have to add some and test to see what's really true. So, assuming you add 4 ppm FC each time you add chlorine, you should stop using Dichlor after 5 additions (at the most). The combination of 20 ppm CYA with 4 ppm FC chlorine is the minimum needed to ensure that you kill the bacteria Pseudomonas aeruginosa that causes hot tub itch. If you want to be more conservative, you can stop the Dichlor after 3 or 4 additions of 4 ppm FC each (so you would be at about 11 or 14.5 ppm CYA). Also note that if you remove your spa cover about 5 minutes before you use the spa, then the smell of chlorine should be mostly dissipated. Note that though the initial addition of Dichlor is slightly acidic, the process of using up chlorine, whether through disinfection or oxidation or outgassing, is an acidic process. This is not true of your subsequent addition of chlorine using 6% bleach (which is 6% by weight, but really 5.7% available chlorine) which is alkaline/basic. It turns out that the acidity of using up chlorine exactly counteracts the alkaline/basic nature of the bleach so that, on balance, using bleach is pH neutral (in spite of what pool and spa stores say). So, any pH changes you see in your spa are due to other factors such as outgassing of carbon dioxide which is why you use the lower TA level of 70 ppm. Over time, you will get a feel for your spa and how often you need to add bleach and probably a little acid. Just make sure that the FC level is at least at 4 ppm at all times. It takes 2.7 fluid ounces of 6% bleach to add 4 ppm FC to your 350 gallon spa. I hope that helps. Let us know how it works out for you and if you have any more questions.

1. Do not know, but ozone is a strong oxidizer and may break down softsoak (Biguanide). Since Biguanide is incompatible with chlorine and bromine, I suspect it is not compatible with an ozonator. You'll have to ask someone more familiar with that combination. 2. The Taylor K-1725 test kit will test both Biguanide and Hydrogen Peroxide (both are needed and apparently provided in the multi-part softsoak system). However, it is an expensive kit (almost $100) so you might find a less expensive one elsewhere. 3. Bacteria tests are not generally available. Algae you will see while the bacteria that causes "hot tub itch" you will feel, though not everyone is as sensitive to it. If you maintain proper Biguanide and Hydrogen Peroxide levels, I think your spa will be disinfected -- don't worry about that. The major complaints with the Biguanide system (regardless of manufacterer) are more expensive than other sanitizers, may require special filter cleaning (or replacement), and foaming. I've seen posts of a few users who had algae slime that didn't go away, but that could have been too low levels of Biguanide. However, some users are quite happy with the system. It generally isn't used in pools because of the buildup of chemicals, but in spas you change the water completely every few months so this is not a problem.

You are right that the MSDS refers to PHMB (which is Polyhexamethylene Biguanide) in their MSDS so that the full chemical name must be what they list and I referred to above. I checked the chemical formula for PHMB and it matches what is described in the full chemical name so you are right and I've corrected my post above. Now what is strange about that is that PHMB is similar in many respects to an algaecide such as PolyQuat and that may be why it is not as effective against viruses as against algae and bacteria. That's what fooled me into thinking that this couldn't be PHMB (Biguanide) since that is touted as such a great sanitizer when in reality it may not be quite as good as advertized. I'd like to specifically see CT (concentration times time) constants for Biguanide against the bacteria that causes Hot Tub Itch. Thanks for correcting me and being more thorough at looking at the MSDS. [EDIT] I found the following document at this link that describes more detail about how PHMB should be used, but note that its references are mostly to manufacturers (the 4th reference is not). It normally is not used by itself but in conjunction with hydrogen peroxide. That makes more sense since hydrogen peroxide is a decent oxidizer and would also kill viruses that PHMB may not. It also notes that in pools, an additional algaecide such as PolyQuat is also used. Even the linked document isn't fully accurate since it talks about Trichlor implying that so long as you maintain 1-3 ppm FC then you have effective sanitation, which is most definitely not true if the CYA levels are high. They refer to "numerous laboratory and field studies" that show that 1-3 ppm FC is fine so long as the CYA is less than 150 ppm, but that is also simply not true as can be seen from the Commercial Spa study found near the end of this link where you can see that there is significant bacterial growth in spas with 130 and 150 ppm CYA and over 1.2 ppm FC. This Commercial Spas Study was one of the main studies used to justify 650 mV as the minimum level of measurement by ORP sensors for sanitized water. Also, it takes more sanitizer to prevent algae growth than it does to kill bacteria and viruses so typically pools with too much CYA and not enough chlorine to compensate end up with algae before they become unsanitary. [END-EDIT]

Sorry, I meant SoftSoak, not SoftSwim, though they both contain the same ingredient. Look at this link to the MSDS for SoftSoak and this link for the MSDS for SoftSwim and you will see that they are the same and are a completely different chemical (that is similar to polymeric quatenary ammonia compounds such as PolyQuat 60%) than BaquaSpa such as found at this link. For comparison and a guide of what to look for on the ingredients label (or in the MSDS), here's a sample: [EDIT] The following is now corrected as I incorrectly thought that SoftSoak/SoftSwim were not Biguanide. [END-EDIT] SoftSoak, SoftSwim "B", BaquaSpa which contain the following which are different names for the same thing: Poly(iminocarbonimidoyliminocarbonimidoylimino-1,6-hexanediyl), hydrochloride Polymeric Biguanide Hydrochloride Polyhexamethylene Biguanide (PHMB) PolyQuat: Poly(oxyethylene) (dimethylimino) ethylene (dimethylimino) ethylene dichloride The "Poly" in all of the above means that these are all polymers -- very long-chain molecules with repeated units. This is what makes these chemicals viscous and slow to circulate evenly in pool and spa water. The "imino" in both Soft Soak and PolyQuat are ammonium groups with a net positive charge, aka cationic. This makes both of these compounds effective at preventing algae growth and they are also good clarifiers (i.e. they tend to clump suspended solids in water together so that cloudy water can get cleared through filtration). Sorry for my typo about SoftSwim. SoftSoak and SoftSwim "B" (being the disinfectant of the 3-step package) are the same chemical. [EDIT] It seems that there is this misconception that the residential pool and spa market is regulated by some government agency and therefore that products that claim to be sanitizers are effective. That is simply not true. Only the commercial pools and spas are regulated in both sanitizer usage and dosage by individual state health departments and nearly all of them require chlorine to be used for outdoor pools and spas and either chlorine or bromine to be used for indoor pools and spas, though lower levels can be used if they are supplemented by ozone or ultraviolet systems (but the main body of pool water MUST have a powerful disinfectant and that is almost always chlorine). It is true that for residential use, sanitizers are registered with the EPA and show some disinfection capabilities against bacteria, but there are not dosage recommendations in that case for specific bacteria (such as the one that causes "hot tub itch"). The main reason that only the commerical market is as tightly regulated is one of risk and liability. Because of the much heavier usage (bather load) in commercial pools and spas and because many more people are exposed to the water, having proper disinfection is more important. For example, the transmission of viruses , bacteria or protozoa in a commercial setting is clearly of greater concern since one person could infect many while in a residential environment the odds are that most people using the pool or spa are in the same family anyway where close contact is likely to be transmitted. Of course, the main difference in a pool or spa is that viruses, bacteria or protozoa that are only transmitted by feces are more readily transmitted in bodies of water. Cholera (a bacteria) and other diseases were prevalent until water sanitation was done. Also, because residential pools (though not spas) are not used as heavily, it isn't as critical that the disinfectant be very fast since there is more time available to kill it (since the pool isn't in constant use). Residential spas, on the other hand, have a very small volume of water that is tailored to the number of people able to be in the spa so in this environment it is more important for sanitation to work more quickly, though still not as quickly as in a commercial spa which may get use throughout the day or certainly for many hours at night. In a pool environment, the typical problems are algae and that won't kill you or make you sick, but is something that will scare people into buying expensive chemicals to prevent and to treat when all that is needed is the proper level of chlorine. Many people will report that they have no problems using their particular form of sanitation. A lack of problems does not prove that a particular sanitizer is effective. There is no spontaneous generation of organisms so if they aren't there to start with they won't magically appear, but if they do exist (or get blown in by the wind or debris or passed into the water from a body) then they are more likely to thrive in an environment without good disinfection. One needs to look at the cases where there are problems and then see the causes and prevent them. Some people using spas report getting "hot tub itch" which is caused by the bacteria Pseudomonas aeruginosa (which is a hearty and hard-to-kill bug) and this has never been the case in properly sanitized spas. For example, the constant use of Dichlor for sanitation will lead to ineffective disinfection since Dichlor has both chlorine and Cyanuric Acid (CYA) with the latter significantly reducing chlorine's effectiveness and yet there are several spa products that are simply Dichlor. See this post on this forum for more info about the problems with having too much CYA. I could go on, but I think I've said enough. [END-EDIT]

[EDIT] I was wrong about what I said in this post about SoftSwim since it is indeed the same as BaquaSpa (both are Biguanide) and is also the same as SoftSoak which is what I meant originally, so ignore it and read later posts. [END-EDIT] SoftSwim and BaquaSpa are not the same thing. SoftSwim uses a chemical that is essentially an algaecide (a different chemical than found in PolyQuat 60%, but not that dissimilar except that the concentration of the chemical in SoftSwim is only 20%) and as far as I can tell has not been shown to be a good disinfectant -- that is, I don't see where it effectively kills bacteria and viruses. BaquaSpa is a Biguanide so is one of the three main disinfectants referred to earlier, though it has not been shown to be effective against viruses (though it does appear to be effective against bacteria and algae). Only bromine and chlorine are effective disinfectants against both bacteria and viruses and also prevent algae. Also, bromine and especially chlorine are generally less expensive though in a spa this isn't as much of a consideration as with a pool.

Tim, If you have some jets running or other form of circulation, you can test the water after just a few minutes (say, 5 minutes). In a large pool with the pump running, most easy-to-mix chemicals such as chlorine are dispersed rather well in 15 minutes and after 30 minutes are pretty much thoroughly mixed, so in a spa I would expect this to be much, much faster due to the much smaller water volume. pH changes tend to take a little longer to stabilize, but again in your spa it shouldn't take very long. As for how much to add, I can roughly calculate that for you, at least for some chemicals, given your spa's 300 gallon volume. If your fill water (that you can test directly) already has some Calcium Hardness (CH) to it, and if you have no plaster/gunite/grout surfaces (including tile with grout) and if your heater is corrosion resistant, then you probably do not need to add any extra calcium. If you do, then it would take 8.8 ounces (weight) or about 4 fluid ounces (8 tablespoons) of anhydrous calcium chloride or 10.3 ounces (weight) or 12 fluid ounces (24 tablespoons) of calcium chloride dihydrate to add 200 ppm, but you need to reduce this proportionately based on how much CH you already have (so if you already have 50 ppm, then you add 150 ppm which would be 150/200 of the amounts I gave you). To add 70 ppm to TA, you would add 4.75 ounces (weight) or about 2 fluid ounces (4 tablespoons) of baking soda (sodium bicarbonate), but again this assumes you are starting from 0 ppm TA so scale down accordingly depending on the TA of your fill water. You will probably need to add a little acid to bring down your pH. If after the above your pH is 7.8, then to get to 7.5 you need to add 0.24 ounces (weight) of sodium bisulfate acid or 0.092 fluid ounces (about half a teaspoon). However, since I have no idea what your starting pH, TA and CH will be, I can't tell you what you will need to do for pH, but this example should give you a rough idea. For chlorine, adding 4 ppm FC takes 0.29 ounces (weight) of Dichlor. I don't know the density of your Dichlor product but the MSDS says it is 56-60 pounds per cubic foot which is about 0.97 ounces (weight) per fluid ounce (seems a little low to me as that is the density of water) so this is about 1.7 (one and two-thirds) teaspoons. After you switch to bleach, it takes 2.5 fluid ounces (5 tablespoons) of 6% bleach for this same 4 ppm FC. As for frequency of addition, that is something you will have to see for yourself by measuring chlorine levels. You can add the chlorine before you get into the spa and adjust other chemicals that way as well. You don't have to adjust afterwards. Just make sure that each time you go in you have enough chlorine. You'll have to see how much chlorine loss there is each day and you can maintain a higher level to account for this loss -- so start at 8 ppm FC and then add more when it gets to 4 ppm FC, for example. Once you get used to your spa's chemical pattern, you won't have to add chemicals as often, but I doubt that you'll be able to maintain your chlorine over a week. Sweating in such a small volume of water will use up chlorine rather quickly. As for how often to test, that really depends on how quickly your spa's chemistry changes, so just like the chemical additions above, you'll have to get a feel for that over time. Initially, test each time you get into the spa -- at least test the chlorine level. The pH is the next thing that is most variable so test that as well, especially since you've had such pH swings in the past. The TA level won't change very fast and the CH will change the least as will the CYA so really it's just about testing chlorine and pH levels. I can't say how frequently you'll have to do this, but initially test every day, get a feel for the rates of change, then test less as you feel more comforable. Hopefully you will get to a point where a fairly regular and constant addition of some chlorine and a little acid will be what is needed. By the way, you said you added about 2 pounds of sodium bisulfate over 2 months so that would be about half an ounce (weight) per day. This would roughly correspond to the amount of acid needed (at 125 ppm TA) to go from a pH of 7.9 to 7.5 so that sounds about right if you were fighting a strong pH rise. Hopefully, the lower TA of 70 ppm will cut down this rise, though it won't eliminate it.

Tim, Spaguard chlorinating concentrate is nothing more than the Dichlor form of chlorine that contains BOTH chlorine AND Cyanuric Acid (CYA). You should not use this product exclusively -- use it the first few times and then switch to regular bleach (unscented). The reasons for this may be found in this thread on this forum. SoftSoak is sold as a sanitizer, but is really more of an algae preventative and not as effective as a disinfectant. It is quite acidic which is why you didn't have the pH rise as much before (and is why you needed a high TA of 125 ppm). [EDIT] Actually, the MSDS says that it is not acidic with a pH of 7-8, but the chemical composition looks to me like it would be. [END-EDIT] The easiest way to lower the amount of rise in pH in your spa is to lower your TA level to around 70 ppm (only to be done when you no longer use an acidic form of chlorine, which is what you will be doing now). I describe how to lower the TA in the link I gave above. The pH rise is due to the outgassing of carbon dioxide from your spa when you aerate your spa each day when you use it. In essence, the spa is "over-carbonated" so it gives off carbon dioxide just like a carbonated soft drink would and this makes the pH rise. As for test strips, waterbear might be able to offer some suggestions for that, but I would get the Taylor K-2006 test kit instead since you will be able to accurately measure your chlorine levels with the FAS-DPD drop test for chlorine in that kit which will also test for pH, TA, CYA, and CH. Since your CYA will be kept very low (20 ppm or lower), you won't be able to test for it readily (the test only starts measuring at 30 ppm, but a cloudy water test even without the black dot disappearing means that some CYA is present at a level near 20 ppm). If you refill the spa, then you start out by adding calcium chloride to raise CH (to 200 ppm -- but if your spa heater has corrosion resistent cupro-zinc [EDIT] I meant cupro-nickel [END-EDIT] in the heat exchanger and you have no exposed grout/plaster touching spa water, then you may not need to add calcium higher than is what already is in your fill water) and Baking Soda (sodium bicarbonate) to raise the TA (to 70 ppm) and some acid (sodium bisulfate) to lower the pH (to 7.5) and of course some Dichlor for chlorine (to 4-8 ppm FC). Then after that, just add some Dichlor (the first few times -- not more than the equivalent of 20 ppm Free Chlorine amount cumulative) or bleach after each use. Check the FC level before you get into the spa to make sure it is high enough (after you've switched from Dichlor to bleach, the FC level should be at least 4 ppm -- not more than 8 ppm) and test the Combined Chlorine (CC) level to see that it is less than 0.5 ppm (if not, then you need to add chlorine (bleach) to shock with 10x the amount of chlorine as the CC level -- this should happen infrequently if you maintain your FC level consistently). You do not need to use the Nature 2 system (which is just metal ions such as copper and/or silver) if you maintain proper chlorine levels and keep your CYA low (which you do by only using Dichlor a little and then switch to using bleach).

Reese, I'm not sure if you will be able to access this link as it is only accessible for U.S. users (non-U.S. IP addresses are blocked from the Pool Forum website due to previous hacking). The issue isn't that you can't use Dichlor up to 100 ppm CYA. It is that higher levels of CYA require higher levels of chlorine for equivalent disinfection. Also, in spas, the bacteria Pseudomonas aeruginosa that causes "hot tub itch" needs much higher levels of chlorine to kill compared to chlorine levels normally achievable in the presence of CYA. This essentially means that you have to limit CYA to low levels in a spa OR if CYA levels are high, then you need to use very high chlorine levels. This link from the Professional Pool Operators of America (PPOA) also talks about the significant reduction in chlorine's effectiveness when in the presence of CYA. The best fact sheet that talks about CYA and recommends not using it in spas is found at this link from the Department of Health for Pennsylvania. Even this fact sheet is inaccurate in the way it describes the "weak bond" between chlorine and CYA. The truth is that the bond is only moderately weak or strong such that having higher levels of CYA relative to chlorine (say, 30 ppm CYA and 5 ppm FC) has over 95% of the chlorine bound to the CYA in chemicals that are called chlorinated isocyanurates. I have a strong interest in pool water chemistry and worked out all the chemical equilibrium equations and species in a spreadsheet that is found at the first link I gave above. The source information for the equilibrium constants may be found on PDF page 18 (document page 12) at this link. I also went to an off-site library to look at the original source document for these equilibrium constants that were determined by scientists in 1973 and presented at a conference in 1974 as follows: J. O'Brien, J. Morris and J. Butler, “Equilibria in Aqueous Solutions of Chlorinated Isocyanurate”, Chapter 14 in A. Rubin, ed., Chemistry of Water Supply, Treatment and Distribution, 1973 Symposium, (published 1974), Ann Arbor Science, Ann Arbor, MI, pp. 333-358. In this original source document from 1973, the authors recommend a CYA level of no more than 25 ppm for pools. I have also been in contact with the company that makes Dichlor/Trichlor (Oxy Chemical; Occidental Petroleum) as well as ORP sensor manufacturers. There are financial (economic) reasons that only partial truths and limited information is given with regard to the relationship between chlorine and CYA, but it isn't that the science isn't known. At least that is my opinion of what is going on. The best information I could find on the CT constant for "hot tub itch" ranges from around 30 to 50 which means that to kill this bug in one minute takes 30-50 ppm FC (or possibly disinfecting chlorine level since the pH was not given for these CT constants). To kill the bug in an hour takes around 0.5-0.8 ppm FC which doesn't sound like much, but you need to understand that CYA significantly cuts down effective chlorine concentration. A rough rule of thumb applicable at a pH near 7.5 and when CYA is at least 5 times larger than FC is that CYA cuts down effective chlorine concentration by a factor equal to the CYA ppm rate. So a CYA level of 30 ppm cuts down the effective chlorine concentration by (more than) a factor of 30. Yes, that is not a misprint -- it's how the chemistry works. Fortunately, most bugs in pools are relatively easy-to-kill so the combination of 30 ppm CYA with 3 ppm FC results in 0.04 ppm of the disinfecting form of chlorine (hypochlorous acid, HOCl) and is equivalent to about 0.1 ppm FC if no CYA were present. This represents an Oxidation-Reduction Potential (ORP) of around 675 mV which is above the minimum 650 mV needed for disinfection, but it takes more chlorine to prevent algae than the 650 mV disinfection minimum. Now for a spa, the hard-to-kill "hot tub itch" bacteria means one should have an effective FC level of at least 0.1 ppm FC if one wants to kill this bug in a 4-8 hours or so (and even that may not be fast enough to overcome normal bacteria growth rates). This corresponds to an FC level of 4 ppm with a CYA level of 20 ppm. This is why I recommend only using Dichlor a few times to have no more than 20 ppm CYA and then to switch to bleach. As for TDS levels, you have been misinformed. Different levels of chlorine provide different levels of TDS, CH, CYA as shown in the following table that accounts not only for the addition of the chlorine source, but also the using up of chlorine (which is an acidic process) and accounts for the acid or base that must be added to restore pH. Increase in TDS, Calcium and CYA with 1 ppm FC increase and usage Type of Chlorine TDS CH CYA Acid/Base Bleach / Liquid Chlorine 1.6 0.0 0.0 Slightly Basic SWG 0.0 0.0 0.0 Neutral to Moderately Basic* Calcium Hypochlorite 1.2 0.7 0.0 Slightly Basic Trichlor (tablets) 1.4 0.0 0.6 Very Acidic Dichlor (granular) 1.8 0.0 0.9 Moderately Acidic Chlorine Gas 1.6 0.0 0.0 Extremely Acidic *SWG varies in its tendency to increase pH and therefore the amount of acid needed to remain neutral. The pH rise (probably from outgassing carbon dioxide due to aeration from the hydrogen bubbles created in the SWG) and added acid to restore pH will increase TDS, but is not shown above since it varies by pool. Dichlor increases TDS more than bleach (due mostly to the CYA added from Dichlor). Some of the TDS will not be measured by a conductivity meter since some of the CYA is in a neutral form (i.e. is no a charged ion). The TDS from bleach after the chlorine is consumed is in the form of salt (sodium chloride, NaCl). Also, it is a misconception that using bleach or chlorinating liquid is strongly basic/alkaline. Though the initial addition is basic/alkaline, the consumption of chlorine is acidic and these nearly exactly cancel each other out so that the net effect is almost pH neutral. The chemistry involved with this may be found at this link (only accessible in the U.S.). If you look at my first link at the start of this post, you will see that the typical rise in pH found in many pools and spas has to do with the outgassing of carbon dioxide. This is why it may seem like Dichlor is pH neutral when it is not. There are also better ways of keeping the pH from rising as much, namely lowering the TA to as low as 70 or 80 ppm, not trying to force the pH below 7.5, and minimizing aeration (which is hard to do in a hot tub). As for the shelf life of chlorinating liquid and bleach, this is very much a function of temperature and chlorine concentration (half the concentration lasts 4 times as long), but generally speaking 12.5% chlorinating liquid will lose its strength rather quickly if kept in the sun, but in shade (less than 80F) it will take over 6 months to lose half of its potency (see this link for a useful chlorinating liquid half-life table). In practice, it's a good idea to use chlorinating liquid within a month of its purchase. I have tested the 12.5% chlorinating liquid that I buy from my pool store and it is always at or near full strength, but they keep it in the shade and have good turnover. Bleach in the stores loses its potency much more slowly, as long as it is well capped (sealed). It is more important that you pay attention to the bleach concentration on the bottle as cheap bleaches may only be 2-3% chlorine. Clorox Regular unscented bleach is 5.25% while Clorox Ultra unscented bleach is 6% chlorine. I don't want to overwhelm you with information, but want you to feel comfortable that the advice of either not using or minimizing the use of products with CYA in spas is correct. If you want to have 100 ppm CYA in a spa, then to kill the bacteria that causes "hot tub itch" you would need an FC level of at least 20 ppm FC and possibly more. The absence of bacteria, just like the absence of algae in a pool, does not mean that your pool or spa is sanitized or will prevent algae growth. It just means you were lucky or found no symptoms.

As for never using bleach in your hot tub, that is very very strange since Dichlor produces the exact same hypochloric acid as found in bleach. The only difference is that bleach is more basic/alkaline. When you add the bleach, just take care not to pour it concentrated directly onto any hot tub surface. If you are afraid you can't add it to the water carefully (mixing it with some circulation), you can add it to a bucket of spa water first and then add the bucket of water to the spa. 1. It takes just 3 ounces of 6% Ultra Bleach or 3.5 ounces of 5.25% regular bleach to get to the minimum of 4 ppm FC in 360 gallons. This should be equivalent to 0.35 ounces (weight) of Dichlor. Since you will lose some chlorine between the times you add it, you could add a little more -- say, 5 ounces to get to around 7 ppm FC. With the 20 ppm CYA in the pool (after you use Dichlor a few times), the effective disinfecting chlorine level will only be around 0.16 ppm which should be enough for good sanitation (though it will take about 4 hours to kill the "hot tub itch" bacteria at this level of chlorine, but that should be OK since you aren't using the tub all the time as would be the case with a commercial spa). Try getting your pH to 7.4 before you add the chlorine since it will make the pH rise initially, though it will drop down again as the chlorine gets used (assuming we tackle your carbon dioxide outgassing issue through the lower TA of 70 ppm). 2. Technically, you should not need to do a weekly shock if you maintain proper chlorine levels since breakpoint should occur somewhat continuously. If you have a good chlorine test kit (such as the Taylor K-2006 with FAS-DPD drop test for chlorine), then you can test to accurately see your Free Chlorine (FC) level as well as your Combined Chlorine (CC) level. This latter CC level should be less than 0.5 ppm in which case you don't need to shock. If you do find it higher, then you could shock with 10x the amount of chlorine as the CC measurement (so if CC is 1.0, then use 10.0 ppm FC to shock). 3. I would not use your Nature 2 stick at all. I believe it is just copper (and/or silver) and though that does some disinfection, it obviously wasn't doing you any good for Hot Tub Itch. The chlorine should be plenty for disinfection and oxidation as long as you maintain its level (which it sounds like you would do by daily addition and/or checking). 4. Yes, you can get 4 months out of your hot tub since that is a function of how often you use it. Typically, people that use it every day aren't able to go that long, but this varies by hot tub usage. How do you tell when you need to change your hot tub water? 5. You could use bromine instead of bleach (you would still use bleach to activate the bromide to bromine), but that gets more complicated since there are different kinds of bromine systems you can use. waterbear can tell you a lot more about those options as he is much more familiar with them than I am. I believe you will be happy with using chlorine. It is safe and effective. The main complaint from some people is some chlorine smell, but that is if they use only chlorine without any CYA and you will be starting with Dichlor so will cut down the active chlorine concentration somewhat which will cut down the chlorine smell. With bromine, some people find that it irritates their skin, so try the chlorine first and see how it works for you -- if it doesn't work out, then you can try bromine instead (with help from waterbear). Technically, you HAVE been using chlorine already -- it's just that with Dichlor the CYA in it cut down the effective disinfecting chlorine concentration way, way down after about a week of adding it to your spa so after that you were essentially using your tub with minimal disinfection (which is why Hot Tub Itch bacteria persisted).

Well, it turns out I can answer you anyway as I'm back from getting food. I know what the problem is. You cannot use Dichlor as your sole source of sanitation. Dichlor contains both chlorine AND Cyanuric Acid (CYA) and while the chlorine gets used up sanitizing your pool, oxidizing organics, and outgassing, the CYA does not break down and it just builds up. For every 1 ppm FC you increase using Dichlor, you also introduce 0.9 ppm of CYA. The CYA will reduce the effectiveness of the chlorine so after a few uses, the chlorine will no longer be able to disinfect your spa. So, what you need to do is replace your spa water, then use Dichlor for a few times in the spa and stop using Dichlor when you have added enough for 20 ppm FC. Then, use regular (or Ultra) unscented bleach as your sanitizer from then on until you change the water again in about a month (or whenever you change your water). Oh, and since you will have to replace your spa water, don't bother with lowering the TA. Just add less baking soda (sodium bicarbonate) when you replace your spa water so you just get to 70 ppm TA. And last, but not least, do not use Dichlor for shocking -- use bleach instead. You don't want your CYA level to get much above 20 ppm and you'll want to maintain an FC level of at least 4 ppm minimum. I looked up this "Vermont Method" which just uses Dichlor after every use and for shocking and that is a terrible, terrible method, due to the buildup of CYA -- especially for a spa that needs higher disinfection levels since the bacteria that causes hot tub itch is hard to kill.

CapMorgan, You need to lower the TA in your spa and also target a higher pH of 7.5 or 7.6 or even 7.7. The itching isn't from the pH, but probably with bacteria that causes Hot Tub Itch and that would mean that your sanitation levels are too low. What do you use for sanitation? To lower your pH, you keep the pH low while aerating your water (just turn on the jets in your spa). This will make the pH rise so keep adding acid to keep the pH low (around 7.0 or so) and measure the TA which you will see drop (at the same pH). When the TA gets to around 70, stop adding the acid and keep aerating which will cause the pH to rise. Stop aerating when the pH is at 7.5. Your TA will now be at 70 and the pH at 7.5 and this will have much less tendency to rise in pH (due to less outgassing of carbon dioxide). I need to go out for a while so maybe waterbear can respond to you after you give some more details on your spa sanitation.

Excellent news, and your most welcome. All that really matters is that you got your problem solved. It looks like the "lower your TA" advice to help slow down the rise in pH has worked again. Though this helps to validate the cause being the outgassing of carbon dioxide, helping you out is even more gratifying. Happy holidays to you and everyone (waterbear, too).

Because you changed the water and used bleach instead of dichlor, you have no CYA in your spa (perhaps some small amount is there as a residual since it can stick to surfaces somewhat). Without CYA, your 6 ppm FC is about 2.5 ppm of the "active" form of chlorine (at spa temps of 104F). If you used Dichlor instead, then for every 1 ppm increase in chlorine, you also get a 0.9 ppm increase in CYA. So adding enough Dichlor to get 6 ppm would give you 5.5 ppm CYA and would result in about 1 ppm of the "active" form of chlorine, at least the first time you add Dichlor. Over time with each addition of Dichlor, your CYA levels increased because it doesn't go away while your chlorine did get used up. So after 6 uses of Dichlor (assuming you use enough to produce 6 ppm FC) you would have had 32.8 ppm CYA and the 6 ppm FC would result in only 0.088 ppm of the "active" form of chlorine. So, the bottom line is that when you use Dichlor, your effective "active" chlorine levels are much lower, especially after a few additions of Dichlor. The smell of chlorine comes from its outgassing out of the water and the rate at which this occurs is proportional to the concentration of the "active" form of chlorine. So with Dichlor, you have less smell because you have signficantly less active chlorine. So what does this mean and is it important? If you use Dichlor exclusively, then you will progressively reduce the amount of "active" chlorine in your spa. If you have too little active chlorine, then you won't get sufficient disinfection, especially to prevent "hot tub itch". On the other hand, if you use only bleach then you will have a lot of active chlorine in your spa which will certainly kill the bacteria that causes "hot tub itch", but will also smell much more like chlorine and will also wear out and fade your bathing suits much more quickly and you will be exposed to more disinfection byproducts. From what I can tell, it takes an absolute minimum of 1 ppm FC at pH 7.5 to kill the bacteria Pseudomonas aeruginosa that causes hot tub itch (I couldn't find definitive CT times, but they appear to be on the order of 50 or so meaning that at 1 ppm it would kill the bacteria in about an hour which is OK for a residential situation). That means an active chlorine concentration of around 0.4 ppm is required. You can achieve such a concentration by have 6 ppm FC with 11 ppm CYA. That basically means you can use Dichlor twice to introduce 6 ppm FC into your spa (each time) and after that you should use a non-CYA source of chlorine, such as bleach. So that is what I would recommend to reduce your smell of chlorine and have your bathing suits last longer and reduce your exposure to disinfection byproducts, while still killing the bacteria that causes hot tub itch. Use Dichlor twice to introduce 6 ppm FC each time and after that switch to bleach. Obviously start over with Dichlor again after you completely drain and refill your hot tub. In your current situation, you can just use Dichlor the next two times you need to add 6 ppm FC of chlorine. If you only need to add less FC, just keep track of the difference (i.e. increase in FC) and use a total amount of Dichlor corresponding to 12 ppm FC before switching over to bleach. (I assume that there isn't anything strange going on such as CYA somehow breaking down at higher temperatures. For reasons I can't explain, waterbear didn't register any CYA even after using Dichlor for shocking and I would have expected some sort of measurement after several uses of Dichlor shock.)