Liquid Chlorine Question

[M Toupin]

Hello all,

We got our spa about 2 months ago and landed here trying to figure out the water thing. It's a lot stiffer learning curve than the dealers lead you to believe IMO... I've been reading through the old posts and picked up a lot of great info which have helped out tremendously to wrap my head around this.

We had a bad session with itch right after we got the spa, which we found out too late, was was caused by no sanitizer. At the time we didn't know any better, we just believed dealers recommendation to just use MPS because "we have an ozinator for sanitation". After the itch session and another trip to the dealer we were told to use dicor to kill the itch which shot our CYA to over 150. Yes, I've figured out my dealer clueless and I won't be getting any more advice from her... Thats' how I found this great forumn!

Anyhow, I've just drained and refilled to fix the CYA problem and want to get started fresh on the right foot. We haven't had any problems with the chlorine to this point (other than the high CYA caused by the dicor). We've decided to give liquid chlorine a try. I've figured out that "Regular" Clorox Ultra Bleach is nothing more than Sodium hypochlorite 6%. My question is how much should I use in our 325 gal spa on a daily basis? I know it will very but what would be a good starting point? 1 Tbs of dicor worked well to maintain 3-5ppm.

Also, I have seen several references to a program named "bleachcalc" though I can't find a good link to it, all the links I've found are dead. Is this program still available and if so were?

Thanks

Mike

[chem geek]

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.

[M Toupin]

Thanks for the advice. I refilled and added 1/4 cup baking soda to bring up the TA which raised it to 30. I added another 1/4 cup today and I'm up to 70 now. I'll add another 1/4 up and see what happens, that should get me in the 110 ballpark. Our water is also very soft naturally in this area (40) so I also added 1/4 cup calcium chloride dihydrate which raised it to 120, another 2 Tbs should get it up to around 150 I think. Ph is 7.6 right now so the extra backing soda should be OK as we had to fight last time to get the Ph to stabilize in the 7.5 ballpark last time. I'll let the Ph go a few days and see if it drops on it's own before I mess with it. I was told that white vinegar would lower the Ph, is this true? If so any idea how much would lower the Ph say .2 in a 325 gal spa?

My last question is about the Chlorine . I added 3 oz of liquid bleach right after the fill in the morning and by 9pm the Free Chlorine was zero so we added another 3 oz after we used it last night. This morning its back to zero Free Chlorine and the Combined Chlorine zero also. I guess I'll increase the bleach to 4 oz and see if that leaves any residual in the morning. The CA says it's zero, but from my understanding the test doesn't register until 30ppm. The CA was over 150 when I drained the spa so I'm sure there is still some residual in the spa as I'm sure I didn't get 100% the old water out. Do you think I would still use Dichlor a few times or do you think there should be enough residual CA in the water?

Thanks

Mike

[chem geek]

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.

[chem geek]

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".

[M Toupin]

Thanks for the advice, I think we have it figured out and under control now. The 1/4 of baking soda did raise the pH and TA a bit, but it's back to a TA of about 80 and a pH of about 7.6. We've had a perpetual problem with low pH so I really wasn't too concerned with the rise. the pH has held for the last 3 days so I'm very happy with that. I used dhicor twice and switched back to liquid bleach now which is also working well. We add 3.5 oz of bleach after getting out of the spa each evening and that gives us a FC of about 2-3ppm the next night before we get in. I think we've just about got the learning curve flattened out, thanks for all the advice.

Mike

[chem geek]

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"!

[M Toupin]

One last question; A friend recommended shocking one week with chlorine and the next with MPS. Is this a acceptable practice and is there any benefits or down sides? He claims the MPS will "oxidize" or eliminate any solids better than chlorine, while the chlorine shock will keep the Combined Chlorine in check. Sounds good in theory, but I can't find anything on it. I do have a large canister of MPS left over from the dealer fiasco so buying more chemicals isn't an issue.

Thanks

Mike

[chem geek]

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.