chem geek

Martin, Let me try and answer your questions below: Is all non chlorine shock based on MPS - I've been looking on ebay but cant find MPS but there are lots of different non-chlorine shocks. Most non-chlorine shock is MPS -- just look on the bottle for something that says "potassium monopersulfate" or "potassium peroxymonosulfate". There are some other non-chlorine shocks that are not the same such as ones that say "percarbonate" or "perborate". Does MPS alter the reading of the FC test on normal test strips or is it just the Taylor kit? That's a good question and I don't know for certain. It most certainly interferes with the DPD and FAS-DPD Combined Chlorine (CC) test. It does not interfere with the Free Chlorine (FC) test so likely does not interfere with the FC test on normal test strips. The main inteference with the CC test is only right after a treatment so waiting 8 hours before doing the CC test is usually sufficient and as I mentioned there is a Taylor K-2041 MPS interference remover which also lets you measure if you have an MPS residual. Do you have any idea where I can purchase the Taylor-2006 kit in the UK please? I called Taylor and you can order from their website http://www.taylortechnologies.com but that would involve international shipping charges and would take longer. They do not sell to pool stores in the U.K. though they are looking into that. That's really too bad because I did a quick look at pool stores in the U.K. online and could only find test strips and not complete tests (or FAS-DPD chlorine drop tests). I didn't look very long so maybe I missed something, but I'm sorry to not find out anything more for you about that. [EDIT] It looks like you can get some decent tests at this link which is mostly PlainTest products. They use tablets instead of liquid, but they do have a separate test for CYA and Calcium as well as the standard Chlorine/pH/TA test and they have a combination kit SP315C. Surprisingly, they don't seem to have a test for Combined Chlorine. This site has a good Lamotte test kit and that includes Combined Chlorine. Lamotte competes with Taylor in the U.S. and they are both good companies with good kits, so maybe that is your best bet except you'll need a separate CYA test so maybe the Lamotte PM 41 combined with the Plaintest SP620 is your best bet. [END-EDIT] I've just refilled the spa and used dichlor to bring the FC upto 6ppm for its first dose - the water has been sitting for 36 hours like that and the chlorine level hasnt dropped yet (But I havent used it either). There is quite a smell of chlorine at the moment but its not too bad. Initially, because the CYA is lower, there will be more outgassing of chlorine and hence more smell. This will decline as you raise the CYA closer to 20 ppm. I dont have any MPS at the moment - can I add this at a later date or does it have to be put in before the chlorine on a fresh fill? Will I need to shock my water every week without MPS? You can add it later, but it is designed to be used before organics get into the spa so is used on a weekly basis. It is not a disaster if you don't use it right away. Some people use chlorine alone and do not use MPS, but it's harder to keep the CC down if the spa isn't exposed to sunlight and since you are also more concerned about health issues, the MPS is useful for eliminating the disinfection by-products. If you keep your FC above 4 ppm at all times, then you probably will not need to shock your water since your water will be "continually shocking" due to the FC residual. If you find that your Combined Chlorine (CC) rises, especially above 0.5 ppm, then you may need to shock with chlorine (bleach, not Dichlor). It really depends on your bather load (how many in your hot tub for how long -- and how much chlorine is in the tub and if it stays above 4 ppm at all times).

I think that BleachCalc has a menu option to use metric units (under More Calcs - Settings). I know that my spreadsheet has that option (units of measure). You are correct that Ben has been out-of-communication for a while. The Taylor K-2006 is your best alternative. It's essentially the same as Ben's kit except the quantities are not as optimized and there are extra acid/base demand tests you usually don't need. Why don't you run a full set of tests on your well water and post them. If it truly has a lot of iron, then you are correct that you'll probably have to add a sequesterant. I'm also interested in the TA and CH levels of the well water -- if they are really high, then you might use the whole house filter to cut these down. The TA can be cut down in the pool using low pH and lots of aeration and adding acid, but the CH is only readily reduced through the whole house filter which replaces calcium, usually with sodium (or potassium) via an ion exchange resin.

I found BleachCalc262.exe on a machine I have so I've uploaded it to this link, but I didn't write the program and don't support it. It's very good, however, though I believe has an error in the Borax Borates calculation.

Your pool dealer is wrong on several counts. It is easy to go from a chlorine pool to a bromine pool. You simply add bromide to your pool and the chlorine will convert it to bromine. The chlorine gets used up and becomes chloride. As the bromine disinfects and gets converted to bromide, any remaining chlorine will reactivate it back to bromine and the chlorine gets used up. So eventually, the chlorine all gets used up. The same thing happens in a spa. One HAS to reactivate bromide back to bromine and this can be done with either chlorine or with a non-chlorine shock (KMPS). Going from a bromine pool to a chlorine pool is hard if the bromine is in the form typically added to spas since it lasts longer in that form. If it's just added to the pool as sodium bromide, then the resulting bromine can be oxidized away through high levels of chlorine and sunlight. It's time consuming and uses lots of chlorine. I don't know why bromine is being suggested for your pool. It's a lot more expensive and the only reason it is usually used in spas is that it doesn't outgas as readily as chlorine (at high temps and high aeration) and therefore doesn't go away as quickly nor smell as much, though this can be partially mitigated by using some (but not too much) Cyanuric Acid (CYA) in a spa. Now for your questions: if using bbb, what do most of you do when you're gone for multiple days...even a week at a time? (if noone else is available to tend the chemicals)? If you use a pool cover, especially an opaque one to UV (most are -- even "clear" pool covers don't let much UV light through) then your chlorine will last much longer. I have an opaque electric pool cover for my pool which is 16,000 gallons and I only lose less than 0.5 ppm FC per day (at around 3 ppm FC total). So you could add a bunch of chlorine (to get to, say, 10 ppm FC) and go away for a week, but probably not much more than that. Using Trichlor in a floating feeder or an in-line feeder is an easy approach. Just make sure your TA is higher and start your pH a little higher since the Trichlor is very acidic (i.e. it lowers the pH a lot). Of course, for every 1 ppm of FC added to your pool from Trichlor, you will also add 0.6 ppm CYA, but for short-term use this is fine (especially if you have splash-out or a sand or DE filter that gets backwashed or cleaned). is it advisable to go ahead and install an in-line chemical feeder and just use it with chlorine tablets (time release chlrorine...i'm told) for those times we're away? It's a decent option. The alternative is to just use a floating feeder -- just make sure it doesn't "park" itself near metal -- that happened to me and rusted out some just under the water bar mounts. if yes...are there correct chlorine tablets available (i.e. sodium hypochlorite) to use in these chemical feeders or are all the tablets trichlor... or dichlor...?(i've read not to use those). The only slow-dissolving solid chlorine is Trichlor (Dichlor and Cal-Hypo are solid, but both are quick dissolving). Sodium Hypochlorite is a liquid only. There are some feeders for liquid chlorine (chlorinating liquid or bleach) available using a peristaltic pump, but these are not common. is another advisable option to install a pricey salt water generator or saltwater chlorinator> i don't think these are routinely used on ag pools, but i've checked with my dealer and they say it's ok to use a chlorine generator (it won't void my pool warranty). Yes, this is another option and yes it costs more, but you get convenience in return. There are some units you can just attach to the inside wall (hanging over the edge) of your AG pool or you can go with the traditional in-line units as the last stage in your plumbing. There are a few things to watch out for with a salt pool having to do with the higher concentration of salt and its effect on hardscape (cement, stone) surfaces and on metal, but metal corrosion is virtually eliminated by use of CYA in the pool, which you will have anyway since it's an outdoor pool. can anyone please send me the bleach calculator as an email attachment? i've tried all the links for the calculator, but they don't seem to work anymore. I don't have BleachCalc, but the spreadsheet I created to calculate pool water chemistry will do most of what you want. It's just not for novices. It's at this link.

Martin, I'm sorry to take so long to respond, but with all the spam that is hitting this forum your post got "lost" so I didn't see it until now. I will try and answer your questions. As for how much MPS to use, you should go by the recommendations on the bottle scaled down to your spa size. Pool non-chlorine shock is usually 1 pound per 10,000 gallons which would be around 0.8 ounces per 500 gallons (or 0.4 ounces in your 250 gallons -- that's about 11 grams). However, spa non-chlorine shock has a recommendation of 2-4 ounces per 500 gallons so that would be 1-2 ounces (28 - 57 grams) in your 250 gallon spa. This would be added about once a week unless your spa isn't heavily used in which case it could be once every two weeks. You can also buy monopersulfate test strips that will show you if you are maintaining a residual in your spa so that might be a better guide (or the Taylor K-2006 test kit can be enhanced with the K-2041 which can selectively measure MPS and remove its interference from the FC/TC test). The sun exposure sounds like it is going through glass so that will cut down the UV that breaks down chlorine so I wouldn't worry too much about that. Besides, your initial use of Dichlor will protect the chlorine from breakdown from sunlight (slowing such breakdown; it doesn't stop it). To keep the smell to a minimum, I suggest that you keep the spa covered when not in use, then remove the cover and open a window for brief ventilation before you jump in. You don't have to keep the window open once you are in unless you find too much buildup of odor -- you'll have to determine that for yourself. Your initial use of Dichlor with its CYA should keep disinfecting chlorine concentrations low enough to keep the odor down to minimal levels. THMs are trihalomethanes that are one class of several chlorinated organic compounds some of which are carcinogenic. You shouldn't worry about that in your spa for two reasons. One is that your initial use of Dichlor means that your spa will contain Cyanuric Acid (CYA) which will make the effective disinfecting chlorine (HOCl) concentrations lower and lower concentration means a lower rate of production of disinfection by-products (DPBs) including THMs. Second, is that your use of non-chlorine shock (MPS) will oxidize organics before chlorine has a chance to combine with them and that virtually eliminates the problem of DPBs and THMs. In other words, you will be quite safe. You will have to find out through experience how frequently you have to add chlorine. Using a spa cover will help significantly to keep the chlorine in the spa when not in use. You should keep a minimum of 4 ppm FC in your spa (assuming the 20 ppm CYA level from the initial Dichlor usage which introduces 0.9 ppm of CYA for every 1 ppm FC that is added) and so long as you initially use Dichlor to get your CYA level up to 20 ppm, then you can have your FC level up to even 10 ppm and be technically equivalent to a spa that has 0.75 ppm FC with no CYA. So I would say keeping your FC in the range of 4-8 ppm is fine. You may find that you need to add more chlorine after every use of the spa since the aeration of jets and your sweating in the spa will tend to use up or outgas the chlorine faster than at any other time. On the other hand, your using non-chlorine shock cuts down chlorine usage. Don't forget that after your initial use of Dichlor for some number of days or weeks (until you've added about 22 ppm of FC to get 20 ppm of CYA), you switch to using unscented bleach (e.g. Regular unscented Clorox). If you splash-out and refill with water at all, you might want to check the CYA level every few weeks to ensure it is still at approximately 20 ppm (it is hard to measure that since most kits measure to 30 ppm so the black dot won't completely disappear in the test at 20 ppm). I suspect that you'll only have to check the CYA perhaps once a month if at all since you will completely replace your water typically every 3 months. I hope that answers your questions. And be sure to report back with how it works out for you, what your chlorine usage is, if it smells, etc. We all learn from actual experiences. P.S. I'm really sorry about your hot tub lung. You can read more about it at this link. Note that they say that "added chlorine loses most of its disinfectant properties at temperatures above 84 F", but that isn't exactly true. At higher temperatures the chlorine will tend to evaporate out of the water so it reduces in concentration and THAT makes it less effective, but in your spa the use of CYA helps slow down this process and besides, you are going to stay on top of the chlorine levels in your spa. You'll see that the CDC recommends 2-5 ppm FC, but they don't talk about CYA. I suspect that most cases of hot tub lung and hot tub itch are from people using exclusively Dichlor in their hot tub and when the CYA gets to high levels, the chlorine disinfection ability is lowered to the point where the bacteria are able to grow. In your case, Aqua Finesse appears to be an enzyme and not chlorine (or bromine or biguanide) so it probably wasn't disinfecting very much at all -- probably enough for easy-to-kill bacteria like E.coli, but not enough for the bacteria that cause hot tub itch and hot tub lung. [EDIT] See this link for an update. Note that the use of Aqua Finesse without a sanitizer is not recommended and appears to be the main problem that led LouMart to get hot tub lung. Aqua Finesse may inhibit biofilms, but it does not kill bacteria quickly enough to prevent their growth. [END-EDIT]

If you keep your TA even lower, say at 80 ppm or 70 ppm, the rise in pH will be even slower and you'll need less acid to compensate for this. It is the combination of high TA, low pH and aeration that causes the pH to rise quickly (due to outgassing of carbon dioxide). It is one of those counter-intuitive facts of pool/spa water chemistry that lower TA leads to more stable pH IF the rise in pH is due to carbon dioxide outgassing. The only time to have high TA is in a pool that uses an acidic source of chlorine, such as Trichlor tablets.

I agree with you that not all types of bleach are suitable for pools (or spas). Scented bleach has additives so should not be used for sanitation. However, Clorox unscented regular bleach is registered with the EPA for use in pools and is why you see the "% Available Chlorine" on the bottle (that number isn't needed for laundry uses). Other than it's lower strength (around 6% by weight, 5.7% available chlorine) it is exactly the same as chlorinating liquid (typically 12.5%, though sometimes 10%). I cannot comment on bleach from Walmart or Kmart, but if it is unscented, it is likely to be OK for pools, but I could be wrong about that -- it depends on what else is in such bleach (other than salt and a little extra sodium hydroxide).

Yes, you've got it. Keeping your TA lower will help you keep the pH more stable (ironcially) or certainly have you adding lower quantities of acid. You can also keep your pH a little on the higher side (say, 7.7 instead of 7.5) and not try to fight so much to keep it down as that will also help (i.e. the rise in pH slows down as the pH gets higher). You can't do much about the aeration since having spa jets is part of the purpose of having a spa, but you can keep your spa covered when not in use as that helps keep the carbon dioxide inside (and you probably do that anyway to keep the spa warm and clean). As for how low to go with TA, it's a dicey decision. I wouldn't ever go below 50 and probably in a spa 70 is a more reasonable lower limit. 80 is fine as well -- just experiment with your own spa to find out what works best for you and if you report back to us with your results, that would be great. You want some TA to be there to buffer the pH from real sources of pH movement that are other than the "higher TA, pH rising" effect itself, such as any acidity or alkalinity introduced from bather sweat, etc.

First of all, I assume that the acid that is being used is probably dry acid (sodium bisulfate) and generally speaking it is always bad to add acid to water and not circulate because the acid will tend to concentrate in one place for too long and can cause damage to surfaces (especially dry acid that must dissolve in the water from its solid form). The safest way to add acid would be to add it to a bucket of water (which dilutes it) and then add that to the main body of water, but that is usually overkill. If you SLOWLY add acid into circulating water it will dilute very quickly. However, in a spa using dry acid, it might not dissolve fast enough so the bucket technique is safer. In a pool adding Muriatic acid (which is a liquid) one usually does not dilute in a bucket and instead slowly adds directly to the pool water. One should add the acid near an output jet, not near an input (suction). In a pool, for example, it is wrong to add acid to the skimmer as this will cause the kind of damage you describe to the pump seals (and to the copper heat exchanger, etc.). You should generally add acid over a return with the pump running. In a spa, this means over a jet with the jets running. By the time this diluted acid gets to the pump, the water will be at near-normal pH. It is true that you don't want to add so much acid as to get the overall pH below 7.0 so in a spa this gets a little tricky, but if you measure first and add less acid than you think you need and you add it slowly and then remeasure the pH, then you can be safe. Now as for the explanation of why aeration helps, both pools and spas are intentionally "over-carbonated" almost like a carbonated beverage. This is done intentionally when you increase Total Alkalinity (TA) by adding sodium bicarbonate (baking soda; Alkalinity Up) after you first fill your spa with water. The TA is there mostly to act as a pH buffer. However, because there is more carbonate (dissolved carbon dioxide) in the water than in the air above it, it will have a tendency to outgas and this process raises the pH while keeping the TA constant. The easiest way to think about it is that carbon dioxide in water forms carbonic acid so when the carbon dioxide leaves the water it lowers this amount of carbonic acid. Removing an acid from the water increases the pH (and the fact that both hydrogen ion and carbonate ion get removed simultaneously keeps the TA constant due to the technical definition of TA and how it is measured). The lower pH forms more carbonic acid in the water from the overall carbonates (mostly bicarbonate) that is in the water and this higher amount of carbonic acid means it will outgas faster (since there is more of it than the carbon dioxide in the air). Aeration increases the speed at which the physical process of outgassing occurs (i.e. it moves to restore equilibrium faster). So the combination of lower pH plus aeration drives out the carbon dioxide from the water faster, and this outgassing of carbon dioxide causes the pH to rise. When you then add some acid to lower the pH back to where it was (7.0), you lower the TA as well. The net effect is that you lower the TA. After you have lowered the TA to where you want it, you stop adding acid and just let the pH go up with the TA remaining constant. Pool and spas therefore have a tendency to rise in pH and this occurs faster with aeration. Pools with SWG systems tend to show a greater tendency to rise in pH and I believe this is due to the increased aeration that comes from the hydrogen gas bubbles produced by the SWG (in the electrolysis in the SWG, chlorine is produced at one plate while hydrogen gas is produced at the other). It is an ironic and very counterintuitve truth that lowering the TA will reduce this tendency for the pH to rise and will significantly reduce the amount of acid that needs to be added to maintain pH. This is because though higher TA buffers the pH more, it also outgasses carbon dioxide more causing the pH to rise faster. These two factors compete with each other, but the outgassing is a little stronger than the pH buffering effect. So lowering the TA shows about the same or a little less of a pH rise while if the TA was ONLY pH buffering, one would expect to see larger pH increases with lower TA. The biggest benefit is that far less acid needs to be added with the lower TA though it still needs to be added albeit a little less frequently. I hope that all made sense.

Jim is absolutely correct with his method. The key is adding acid to get to and keep the pH low while aerating the water. If you or anyone else wants to know why this method works so quickly and effectively, let me know and I can tell you. The only thing I can add to what Jim said is that after you achieve your desired TA level, you can stop adding acid and keep aerating (i.e. keep your jets on) and the pH will rise (the TA will remain the same). When the pH rises to your desired level (probably 7.5 or so), then stop the jets, cover the spa, and you're done!

See this thread for more discussion on AquaFinesse. You can see from their website that they say the following: When used in combination with a good working ozone or silver ion system, no additional sanitizers are needed. However, the National Spa and Pool Institute (NSPI) recommends that hot tub owners maintain a minimum level of 1.5-ppm chlorine in the spa water. To meet these standards, we strongly suggest using the provided sanitizing tablets as directed in the slow-release dispenser. Soon, your water will be in the best shape of its life-no pH products, clarifiers or additional chemicals needed! So it is recommended to have at least some chlorine in the water, mostly to kill pathogens quickly.

You generally do not want to add any organic compounds to sanitized water (either pool or spa) because whatever oxidizer you have in the water (chlorine, bromine, hydrogen peroxide in a Biguinide system, etc.) will get used up oxidizing it so it is just being wasteful and would be unavailable to oxidize anything else (or sanitize, if the oxidizer and sanitizer are the same). Eventually, these added organic compounds will get oxidized (sort of like "burning") or will get filtered, but that just requires more use of chemicals and/or filter cleaning. It won't help your skin much at all as the baby oil will be far too diluted in your spa water. Instead, I suggest you use a moisturizer after you get out of the spa. You could also use moisturizer before you get into the spa as long as you wait long enough for it to absorb into your skin. Organics that are absorbed into your skin are less likely to be released (especially if your skin "needed" the components in the moisturizer). I wouldn't use baby oil for dry skin anyway. Baby oil was originaly intended to keep water AWAY from skin (from baby's bottoms) to prevent baby's well, you know, "stuff" sticking to their bottoms in a moist environment that would create diaper rash. And yes, it can also help to keep moisture in as well (it's a barrier both ways). Mosturizer's are designed specifically to help dry skin. Applying it after getting out of a spa would be most effective since your skin's pores will already be open and will accept moisturizer more readily. I suspect that any dryness after getting of the spa is not due to your losing the moisture while in the spa (though you do sweat), but may be due to your losing additional moisture when you get out of the spa as your pores are still open, you are still hot, and the water evaporates away. And of course, the hot spa temperatures cause you to sweat so you should be drinking lots of water to replenish that. I just realized that the baby oil you were considering using was probably only for putting into the spa and you may not have been using that afterwards and used a moisturizer instead. Sorry I didn't figure that out from your post initially. Anyway, don't add baby oil to your spa.

My wife has personal experience with the effect of high chlorine with respect to CYA levels. Her swimsuits degrade (usually the rubber degrades before the fabric fades) over just one winter use in an indoor pool, but over a summer of use in our outdoor pool there is no degradation whatsoever. This pattern has been repeated for over 3 years now. What's the difference? The indoor pool doesn't use CYA while our outdoor pool does. The FC levels of both pools are probably comparable in the 3 ppm range (maybe more for the indoor pool -- I need to go over to the community center and test it one of these days). Even if both pools had 3 ppm FC, my pool with about 20 ppm CYA has about 1/20th the amount of disinfecting chlorine compared to the indoor pool with no CYA. That's 1/20th the amount of disinfection, oxidation, algae prevention, and swimsuit degradation capability. As waterbear points out, you needn't worry about chlorine levels in a pool with CYA. The actual hypochlorous acid that does the oxidation of swimsuits is FAR lower than found in pools without CYA.

You will notice that in the Cleanwater Blue system it requires the use of chlorine (in the form of Dichlor) at least initially in addition to its use of copper ions. The EPA registration simply means that it can be used as a disinfectant. It does not mean that copper alone is as effective as copper with a small amount of chlorine and typically chlorine amounts are reduced by up to 80%, but are generally not suggested to be eliminated. Copper doesn't break down organics which is why the Cleanwater Blue system requires regular use of a non-chlorine shock (typically potassium monopersulfate). I'm not going to bore you with all of the violations of EPA rules by a variety of manufacturers (you can look up Zodiac and others, if you wish), but the EPA requires that copper (and silver) disinfectants for swimming pools still have some residual chlorine (actually, the requirement is that it kill a certain amount of pathogens in a certain amount of time and that generally requires chlorine as copper alone isn't fast enough). Cleanwater Blue technically met that by saying they use Dichlor, but they cheated because the chlorine is not maintained after initial dosage. They probably ran their certification tests after initial dosing, not after many days or a month when the chlorine is long gone. You shouldn't need to use very much chlorine at all, but using none at all is not what the EPA intended. The bottom line is that you are happy with it, but not everyone has had good experiences. Just don't take the manufacturer's referral to EPA certfication as meaning anything more than it is.

Most chlorine-based systems promote the use of Dichlor exclusively and that will very quickly lead to a lack of proper disinfection with the risk of getting hot tub itch (caused by the bacteria Pseudomonas aeruginosa). It isn't the chlorine that is the problem, but the inappropriate recommendation of using only Dichlor. Dichlor contains not only chlorine, but also Cyanuric Acid (CYA) and the CYA does not breakdown or go away the way that chlorine does. So every time you add 1 ppm Free Chlorine (FC) to your spa using Dichlor, you also add 0.9 ppm Cyanuric Acid (CYA) and this CYA can therefore build up very quickly. Chlorine becomes less effective in the presence of CYA so after just a few weeks of using Dichlor, your hot tub is no longer properly sanitized. The correct way to use chlorine in a hot tub is to use Dichlor only initially a few times until you've added about 20 ppm FC cumulative. Then switch to unscented bleach until the next time you drain/refill your spa (at which point you start over again using Dichlor a few times).

[EDIT] I finally found some scientific literature that backs up the Nature2 "low chlorine recipe" that uses Nature2 silver ions with MPS here. The following was written before I found such scientific literature. [END-EDIT] The website (from the link in the first post) indicates that "the active ingredient of Cleanwater Blue is copper ions." They presumably enhance the effectiveness with a molecule that is negatively charged that attracts the copper. I'm not sure how this enhances the effectiveness except possibly to keep the copper from accumulating on some other negatively charged surface (i.e. it may help keep the copper floating more in the main body of water so it can attach to bacteria). The main problem with bacteria in a hot tub is with the bacteria Pseudomonas aeruginosa that causes hot tub itch. This is not an easy bacteria to kill (like E. coli, for example). I tried to look up specific information about this and came up with this link that refers to how copper PLUS chlorine is more effective than either alone. So I would not use this system without also having at least some chlorine. Of course, not every hot tub gets the bacteria that causes hot tub itch (there is no spontanous generation so the bacteria has to come from somewhere initially) and many people use Dichlor only in hot tubs and end up getting hot tub itch because they don't realize how the CYA in Dichlor reduces chlorine's effectiveness. In general, no copper or silver or copper/silver combination system should be used by itself without at least some additional conventional sanitizer (usually chlorine) though the amount of chlorine can be less when using the metals in conjunction.

If I were you, I would not use 100 ppm Dichlor alone. For every 1 ppm of Free Chlorine (FC) introduced by Dichlor, you are also adding 0.9 ppm of Cyanuric Acid (CYA). Though adding enough Dichlor for 100 ppm will kill anything in your spa, it is technically no different in disinfection or oxidizing power than about 13 ppm of chlorine from bleach with no CYA. The problem is that after the chlorine dissipates, you will still be left with 90 ppm CYA! Instead, I would suggest you just start by shocking with bleach alone. You should not need to shock with more than 10 ppm bleach if you do not have any CYA left, though CYA does tend to stick around in pipes and on surfaces, so you could do 20 ppm bleach if you want, but definitely not more than that. After the chlorine gets down to around 5 ppm or so, you can then use Dichlor the first few times, but not more than the amount to cumulatively add 20 ppm FC to your spa. After that, use bleach only -- no more Dichlor -- until you change the water in your spa in a few months. This assumes that you want to switch to using chlorine which, as waterbear pointed out, is something that usually does not cause any problems. With the CYA from the initial Dichlor (for 20 ppm FC) you will have around 18 ppm CYA and by maintaining an FC of 5 ppm this is equivalent to having just 0.27 ppm FC if no CYA were present and that is very unlikely to cause any problems with allergy or skin irritation.

Yes, if your CYA is very high, then 5 ppm FC may not be enough to prevent "hot tub itch" though it should be enough for most everything else. If you have a CYA of 90 then it would take 15 ppm FC to be equivalent in disinfecting and oxidizing power as 5 ppm FC with a CYA of 30 (roughly speaking -- and at a pH of 7.5).

I am going to put your comments in a different font and answer your questions below them. Hope this works. Thank you for your continued patience with me. I wish I was a chem geek Trust me, it has its disadvantages. I didn't get married until I was 38! OK, our tub is brand new..initial filling was 1/2/07, 350 gal, 2 people usage 99.9% of the time So the other day we shocked the spa with non chlorine shock. After 2 days of NON use, we tested the water. Our ph 6.2-6.8 alkalinity 40-80 barely reading chlorine (.5) and the stabilizer is back down to 30-50 Actually I see that the 30-50 is good ...but what made it come down? Non-chlorine shock (potassium monopersulfate, KMPS) is very acidic. However, it should not have dropped your pH that much. 1 ounce weight (which is probably about 1-1/2 tablespoons) would lower the pH by only about 0.1 units. As for the stabilizer, that doesn't make sense at all. I think your next question will help answer these wild variations you are seeing. You may need to add more chlorine than you are doing. Add double the amount, to about 8 ppm FC, and see if that goes down to about 4 ppm FC the next day. If so, then add 4 ppm FC the next day and thereafter. You want to get your chlorine to a point where you add some one day and it doesn't go below 4 ppm FC the next day. Here is probably a stupid question- should we be dipping our strip directly into the spa or collecting water in a cup and testing the water in the cup? Does it make a difference?? These levels are from collecting in a cup It's not a stupid question (there's hardly any such thing). Collecting water in a cup should be fine -- no need to dip test strips directly into a spa. However, it sounds like you are using test strips. These can be very inaccurate (depending on the manufacturer of the test strips), especially for certain tests. I suspect the CYA test readings aren't particularly accurate which is why you saw such a large change. CYA simply doesn't disappear -- there are some anaerobic bacteria that can break it down, but this is usually in pools over a winter (these bacteria are in the ground as well which is why CYA is considered a biodegradable substance). I strongly suggest you invest in a high-quality test kit such as the Taylor K-2006 which has a drop-based FAS-DPD chlorine test, pH, Total Alkalinity (TA), Cyanuric Acid (CYA) and Calcium Hardness (CH). You really can't adjust your water until you know what is really in it. Note that with the non-chlorine shock, that this will get reported as Combined Chlorine (CC) so to eliminate that interference you can also get the Taylor K-1520 reagent that can be used with the chlorine test. Though these kits are a bit expensive up front, they will last quite a while and are absolutely worth it. Remember that some tests are temperature sensitive, such as the CYA test so have your spa water (in your cup) come down to room temperature before starting the test. Ok, so after doing my homework this is what I think we need to do today: retest water ( not in a cup??) if the alkalinity is still low, raise that. How long after adding the product should we retest the water to determine if it is raised to the proper level? My research tells me that adding this (alkalinity raiser)in itself may raise the PH, correct? If not, we then need to raise the PH. How long after raising the PH should we then add the Dichlor to raise the chlorine to 3-5ppm? I wouldn't be so sure that the alkalinity is too low. The test could be wrong. You should keep your TA on the low side so that you will prevent the pH from rising from the aeration from your spa jets which will force more outgassing of carbon dioxide (that's what alkalinity is -- sodium bicarbonate -- so your spa is intentionally over-carbonated like a lovely tasty beverage!). You actually do not want to increase your alkalinity right now since raising the pH (by adding pH Up) will also have the alkalinity rise. The easiest way to get your pH up is simply to run your spa jets and aerate your water. This will outgas carbon dioxide and make the pH rise with no change in alkalinity. Stop aerating when your pH gets to 6.9 and then add 1 ounce weight (a little more than 2 teaspoons) of sodium carbonate (i.e. washing soda which is in pH Up). This will raise your pH from 6.9 to 7.5 while also increasing your alkalinity from 60 to 80. However, doing anything before you get an accurate test kit a very approximate at this point. ok...I am taking a deep breath. Thank you, pmj Your most welcome. You're doing great, so hang in there and come back with more results and questions.

I don't know your hot tub volume, but assuming it is 350 gallons, then 1 teaspoon (not tablespoon) of Dichlor would add about 2 ppm FC (and 1.6 ppm CYA), but you saw much more than that (5-10). Something is really weird here -- there's some information missing because it just doesn't make sense. Are you sure it wasn't a tablespoon you added? If your total chlorine is 7 when your free chlorine is 3, then you have a lot of combined chlorine (4 ppm) and if that is monochloramine, then that smells pretty bad (like a heavily used indoor swimming pool). The chlorine you are adding to your spa, whether it be Dichlor or bleach, is getting consumed by something in your spa. If it were just getting outgassed, it wouldn't raise the Total Chlorine. The chlorine alone is not shocking your spa, but just adding Dichlor won't do that either. You may need to use a non-chlorine shock (potassium monopersulfate, KMPS) and that would be true regardless of whether you used Dichlor or bleach or a mix because your chlorine is not breaking down organics (or ammonia) sufficiently (without exposure to sunlight, this can be difficult -- it takes time and if you use your hot tub frequently, then the non-chlorine shock would be the way to go for shocking -- it breaks down organics readily while chlorine does not, at least not without sunlight). As for what would happen if you just use Dichlor only, your Cyanuric Acid (CYA) level would build up and would combine with chlorine more (including the chlorine that comes from Dichlor itself) so that the amount of disinfecting chlorine in your hot tub would be less and less over time, assuming you kept the same Free Chlorine level. You can compensate for this by increasing the Free Chlorine level. So if you had 3 or 4 ppm FC at 20 ppm CYA, then after another week of Dichlor you would need 6-8 ppm FC at 40 ppm CYA and after 2-3 more weeks you would need 12-16 ppm at 80 ppm CYA and so on. It's not practical at some point so what happens after a month or so is that your disinfecting chlorine level will not be high enough to kill the bacteria that causes "hot tub itch". It should be plenty high enough to kill other bacteria and viruses.

If the Ultra bleach says 6%, then 3 cups in 450 gallons is 25 ppm FC which is really more like a shock than anything else. The half a cup is 4.3 ppm FC and you are adding that twice a day. That is an awful lot. The reason is that you don't have any CYA (it sounded like you don't use Dichlor at all) so the chlorine outgasses very quickly in that case. I'm surprised you don't smell it more. It's also rather hard on your swimsuits at these higher concentrations (without CYA, the disinfecting and oxidizing chlorine concentration is about 20 times higher than the same amount of chlorine with 20 ppm CYA). I would suggest that when you do a fresh fill (or even now with your current fill) that you use Dichlor for a few days for the equivalent of around 15-20 ppm FC. I'll bet your chlorine loss will go down quite a bit after you've used the Dichlor. And yes, you are right that the ozonator may also be lowering your chlorine level somewhat, but I'll bet the bulk of your loss is due to not having CYA in your tub. As for a deposit on the filter, there shouldn't be any if the bleach is unscented. You shouldn't use bleach that is scented or perfumed because it will leave gunk in the filter. Unscented bleach is only sodium hypochlorite and salt. The sodium hypochlorite converts to salt when it gets used up so you just end up with salt and that won't show up in the filter or anywhere else. So if you are using unscented bleach, then the filter gunk is a mystery. jacko, before you switched to trying out bleach, how much Dichlor did you add every day? Maybe your chlorine demand in your spa is just high and it needs a lot of chlorine from any source, Dichlor or bleach, each and every day.

Adding 1/3 pint of 5.25% bleach (which is a little more than your strength) to 350 gallons would increase the FC by over 6 ppm which is quite a lot, especially if done every day. In 500 gallons, it would increase FC by about 4.5 ppm. You could check the chlorine level after adding the bleach and letting it circulate for a few minutes (with some jets on). That'll give you a better idea of the true strength of your bleach and how much the FC goes up with the 1/3 pint you add. Maybe you have the very inexpensive 3% bleach. I would have speculated that its strength was very, very low, but you said you noticed a chlorine smell after adding it. So something doesn't make sense. If there were very little or no CYA in the hot tub, then the chlorine you add would outgas from the tub rather quickly, but with CYA in the tub it shouldn't leave that fast, especially if you put it in AFTER you got out of the tub, turned off the jets, covered the tub (do you cover it?), then tested in the morning. If the chlorine were to leave quickly, it usually would happen with the cover off and the jets running. What kind of chlorine test are you using? Some of them will bleach out with too high chlorine levels having you think there isn't any chlorine when there is actually a lot. The DPD (red color) chlorine test can do that above 10 ppm FC. The OTO (yellow color) chlorine test should be OK with higher chlorine levels (the FAS-DPD test is also OK as it has a flash of color when you add the powder so you can add more if the chlorine is very high). If you are using the DPD test, then you can dilute one part of your spa water with several parts of distilled water (or filtered water) and retest -- if it turns red, then very high chlorine levels were present. That would be more consistent with the strong smell you are experiencing (i.e. maybe you were adding too much bleach and weren't aware of that).

It's really hard to tell what is going on without proper testing. That's why I suggested the Taylor kits, though any you can find that are called FAS-DPD and work by counting drops you add in order to determine Free Chlorine and Combined Chlorine would be good (it's similar to the TA and CH tests in terms of adding drops and looking for a change in color -- in the case of the chlorine test, the color goes from pink to clear). You'll also want to test the CYA level even though it may be lower than the lowest measurement on the test (which is usually 30 ppm). You see, the problem is that if you add more Dichlor, it will tie up more chlorine and that will reduce the smell (assuming it's "clean" chlorine you are smelling), but if you add too much, then you won't have enough disinfection against "hot tub itch" unless you use a lot higher FC levels. On the other hand, if the smell is the bad chloramine (combined chlorine) smell, then shocking is needed and it may be that shocking with the dichlor alone is not effective. It might take a lot of bleach -- usually 10 times the amount of Combined Chlorine. So here are some choices. My preference would be for you to get a good chlorine test kit so you can really get a handle on your pool water and know what to do with confidence. If you don't do that or until you do, you can get some non-chlorine shock, that potassium monopersulfate (KMPS) I mentioned, and use that on a weekly maintenance dosage basis. If the smell goes away, then it was probably combined chlorine and the non-chlorine shock is taking care of it. If it doesn't, then maybe you don't have enough CYA after all and need to add some more Dichlor. The last possibility is that you actually have the right balance right now, but that the chlorine smell is "normal" for a hot tub. That's one of the reasons some people like bromine instead, but then again some people are slightly allergic to the bromine (get rashes, etc.).

If you remove the hot tub cover about 5 minutes before you get in, that should help to dissipate any chlorine that has accumulated. You shouldn't be smelling more chlorine than you did in the first few times of using dichlor, but you will smell more than you would have if you had continued to use dichlor. You might be OK with the 3 ppm FC -- I try to be conservative when it comes to hot tub itch. If you start to smell a nasty chloramine smell (not the "fresh" smell of chlorine similar to fresh bleach), then you may need to shock. The best way to tell, is to test with a good chlorine test kit that uses drop-based FAS-DPD. Taylor has a complete kit, K-2006, that also tests pH, TA, CH and CYA (it only tests down to 30 ppm, but if it's cloudy yet you still see the black dot somewhat, then it's probably around 15-20 ppm). If you already have a kit for everything except the FAS-DPD chlorine, you can get the Taylor K-1515-A. With an accurate chlorine test, you can see if you have Combined Chlorine (CC). The test strips and other chlorine tests (OTO, DPD) are not as accurate.

The terms "dichlor", "dichloroisocyanuric acid", "dichloro-s-triazinetrione" and "troclosene" all refer to the same chemical which is essentially Cyanuric Acid (CYA) that has two of its three hydrogen (at the nitrogen sites) replaced with chlorine. "Trichlor" is similar except it has all three hydrogen replaced with chlorine. The typical "Dichlor" replaces one of the hydrogen of CYA with Sodium and that is what you have, plus the compound also has two water molecules attached as well (i.e. it's not pure). The bottom line is that when you add your Dichlor chlorine granules to water, for every 1 ppm of free chlorine that is added, you also get 0.9 ppm Cyanuric Acid (CYA). The chlorine mostly stays attached to the CYA, but some of it goes into the water as hypochlorous acid (HOCl) which is the disinfecting form of chlorine. Bleach is sodium hypochlorite (NaOCl) and when added to water also forms hypochlorous acid (HOCl), the disinfecting form of chlorine, and this mostly combines with any CYA in the water with some of it staying free to disinfect. The hypochlorous acid from Dichlor and from bleach is completely identical. So the only difference is that with Dichlor you are also adding more Cyanuric Acid (CYA). When you measure "Free Chlorine" you not only measure the actual truly free amount of hypochlorous acid (HOCl) that disinfects, but also the hypochlorite ion (OCl-) and, mostly, the chlorine that is bound to CYA. As the disinfecting chlorine in the water gets used up, it gets replenished from the chlorine that is bound to CYA. So you can look at CYA in the water as being a sort of chlorine "buffer" that holds chlorine in "reserve". The amount of disinfection (and oxidation) capability in your spa is related to the amount of hypochlorous acid (HOCl) only. The CYA reduces the amount of this disinfecting chlorine by roughly the amount of CYA in ppm (at a pH of 7.5). So with 30 ppm, you have about 1/30th the amount of disinfecting chlorine than you would if there were no CYA present. This is why it is very important not to let the amount of CYA get too high and this means one should not use Dichlor as their only source of chlorine or for shocking. On the other hand, some amount of CYA is needed or else the chlorine would breakdown too quickly in sunlight or would dissipate (outgas) too quickly in a hot spa with aeration from jets. The bacteria Pseudomonas aeruginosa that causes "hot tub itch" is somewhat difficult to kill, but a combination of 4 ppm Free Chlorine (FC) with no more than 20 ppm CYA appears to be enough to keep this bug away. This means that after draining and filling your hot tub with fresh water, you should start using Dichlor a few times but not more than the amount that would result in 20 ppm FC so that you make sure you don't have more than 20 ppm CYA. Then, you switch to using bleach from then on (until you drain and refill again). You would also use bleach for shocking, if you need to. If you find that bleach alone is not sufficient for shocking (i.e. if the Combined Chlorine, CC, is more than 0.5 even after shocking) then you can use a non-chlorine shock, potassium monopersulfate (KMPS). The bleach you should use should be unscented. Some dealers will tell you that bleach is not registered with the EPA for use in hot tubs (it is registered for use in pools), but that is not because it does not sanitize. It is simply because the market for bleach in hot tubs is very small and not worth paying for the extra registration costs -- at least that is why I believe Clorox didn't bother (consider how small the amounts of bleach are that you add to a spa compared to what you add to a pool). Hope that helps!