chlorine stabilizer/conditioner: pool water chemistry & help - stabilizing the swimming pool chlorine level

Chlorine stabilizer or conditioner (cyanuric acid) is used, in outdoor chlorine-maintained swimming pools, as a means of helping to protect the chlorine from being destroyed by the Sun's ultra-violet rays. This helps the chlorine last longer and reduces consumption. The level of cyanuric acid is easily determined by a simple chemical test. In northern areas, a range of 20-40 PPM is considered ideal. In sunbelt areas, a level of 40-80 PPM, is recommended for pools not utilizing a stabilized form of chlorine. Levels between 80-150 PPM are above the ideal, but are not considered to be a problem. Higher levels, especially over 150 PPM, are thought to reduce the effectiveness of the chlorine and may require the maintenance of somewhat higher chlorine levels. Every time a stabilized chlorine is added, some cyanuric acid is contributed to the water. The only means of lowering the cyanuric acid level is to replace water. Clicking on the underlined and highlighted "keywords" or "catch phrases," in the archived answers will give you access to additional information on that topic or product. Please refer to the Glossary, if there are terms or phrases that require explanation.

More information about the ColorQ Water Analyzers can be found by clicking on the above image. This hand-held, digital tester requires no color matching or look up charts and performs the following tests: pH, Free & Total Chlorine, Bromine, Total Alkalinity, Hardness and Cyanuric Acid. Be better informed and avoid costly problems!

What is the acceptable level of cyanuric acid in a swimming pool? Someone came out to do a water test and said that my level was 250 PPM, and that I should drain the pool. They said I should not use tablet chlorine - only liquid chlorine or my pool would be ruined in 3-5 years. Is this correct?

A range of 20-40 PPM is considered ideal. In the sunbelt, 40-80 PPM is preferred. There is no question that 250 PPM is much too high. Such levels can interfere with the effectiveness of the chlorine and require you to maintain a higher Free Chlorine level, in order to maintain adequate sanitation. Not knowing where you are located makes my answer more difficult. High levels can lead to other water quality issues in hard water areas. They are telling you not to use chlorine in tablet form because it will add more cyanuric acid to the water. Liquid chlorine does not contain cyanuric acid. I'm not sure about "ruining your pool." I hesitate to tell anyone - especially if I do not know the type of pool or construction to drain a pool. If it is a vinyl pool, completely draining the pool can risk structural damage or liner shrinkage. If the pool is masonry, it should be able to be drained. However, I would double check with the builder. If you don't want to or can't drain the pool completely, another option would be to pump out some water every week - perhaps, up to a foot below the skimmer. This will drop the cyanuric acid level in increments. Once the level is down, I suggest that you use supplement the chlorine tablets with a weekly dose of liquid chlorine, as a means of keeping the cyanuric acid level from rising too quickly. I hope that I have been helpful.

Cyanuric acid is usually tested at the start of the season and is added, if necessary. Most residential pools, using a stabilized chlorine, will rarely have to add additional; product, unless large amounts of water have been lost or displaced. Pools that are maintained on chlorine, but are not using a stabilized chlorine, may have to replenish the stabilizer level from time to time, if water is lost due to backwashing, leaks or overflow. The test is simple and could help reduce chlorine consumption. To better assure proper overall pool water chemistry, visit a pool store that has a very reliable, professional lab such as a WaterLink or Pinpoint system, rather than a less accurate test kit or strip reader. To locate a dealer near you, go to: www.lamotte.com/pages/pool/expdeal/index.html I hope the information proves useful.

My pool water was tested and I was told that the stabilizer level was 200 PPM. I was told that the only way to lower the level was to replace some of the water. Is there a chemical that I can add that will lower the level, without removing water? What happens if I don't lower the stabilizer level? Thank you.

Firstly, there is no chemical that you can add to the water that will remove the stabilizer and lower the level. Such a chemical was marketed, years ago, but proved to be a disaster for the pool owner. Secondly, replacing water is the only effective means of lowering the stabilizer level. Thirdly, if you don't lower the level you will be forced to maintain higher levels of chlorine, in order to provide adequate sanitation. Incidentally, the safest way to lower the water, without potentially damaging the pool, is to lower the water to the winterizing level. Do this weekly, until the level drops below 100 PPM. Testing for Chlorine Stabilizer will help you keep track of the progress. A level of 150 PPM is considered too high. At 200 PPM, you are interfering with the effectiveness of the chlorine. I hope that I have been helpful.

I found your website through LaMotte Company, whose strips I use religiously. I live in Maryland, have a black plaster pool, around 7 years old, use DE filter, and stabilized granular and stick chlorine. This summer we had an unusually hot spell lasting for about 10 days that coincided with an outbreak of green algae, which I’ve never had before. I seem to be using unusually high levels of chlorine as well to ward off the algae, but the chlorine seems to be wearing off more quickly than usual. I’ve had a couple of water tests done at different stores with some varying results. However, I did get similar readings for cyanuric acid (140-150ppm) and stabilizer-adjusted total alkalinity (55-61ppm). Hardness is a little on the low end (200-260ppm), pH is 7.2-7.3. Chlorine readings are as expected low. One test said I had 0.83ppm iron, the other did not detect it. Read your website about cyanuric acid and have concluded I should try to lower the 150 reading. I plan to winterize in about a month (with a professional). My question for you is – does cyanuric acid dissipate over a period of time? If I don’t replace any of the water now before winterizing, will it “go away” over the winter. We usually reopen early April. Your suggestions would be welcome. Thank you.

Bruce V., Maryland, 9/21/2006

Cyanuric acid will not go away. It can be lowered, only by replacement of water. You should lower it to under 75 PPM. High levels will make chlorine less effective, but you will still get a reading. Your problem could be not enough chlorine is being added, for the way your pool is being used. Your hardness is not low and you should not allow it to rise higher, by using calcium hypochlorite. I would not recommend dichlor either, as it will cause the cyanuric acid level to rise. To supplement the trichlor, you should use liquid chlorine or lithium hypochlorite, as neither will add to a buildup problem. The iron should be treated by a double dose of a metal treatment. As long as you are using chlorine, why not make it easier? A salt chlorine generator will do just that and avoid chemical buildup problems. I hope that this information is helpful.

Sincerely. Alan Schuster, 9/21/2006

Hi, you answered a question for me a few weeks ago about our cloudy water after opening, and after giving it time our water looks great. Now I have two problems. After shocking the pool in the evening, we are able to maintain a free chlorine reading of about 4 ppm overnight. I go home at lunch and bring some water back to work with me to test, and verify that the free and total chlorine are about 4.1 and 4.5. But, by the time I get home in the evening the chlorine has dropped to nothing. We have a chlorinator that we keep tri-chlor tablets in but for some reason it doesn't seem to be working. We even added some tablets to our skimmer basket (this is not our normal practice) just to make sure it wasn't the chlorinator. In past seasons, if we loaded our chlorinator up, even at a low setting, it would over chlorinate the pool big time. So we would always keep about two tablets in and this would last 3 or 4 days, even in hot weather. It's still cool (temp is about 65) so why are the tablets not working? Is it time to load the chlorinator up? So every time our chlorine drops to zero, we shock again, and the same thing happens. Our pH is now dropping below acceptable range too. The other question is our stabilizer level. When using the drop turbidity test, results indicate that level is too high and we have been able to get it down to 100, with partial water changes. However, if I test with test strips, they indicate that there is no stabilizer. It doesn't change color at all. All other parameters on the test strip are very close to what I get with a kit, or here at work. If there really was not stabilizer, this would explain the chlorine not lasting right? But I thought the drop turbidity test was most accurate. We have a 24' x 52" above ground pool. Thanks.

The most likely reason that the chlorine levels would drop like that is if there are algae and bacteria growing on the underwater surfaces. If that is the case, you might not notice it, but the walls would be slimy. You need to shock the pool. Once this material is destroyed, the trichlor tablets will be better able to keep up. Trichlor is acidic. You need to add soda ash on a regular, as needed, basis. Have the pool and tap water tested for phosphates and nitrates. You may not be able anything about the nitrates. If present, you positively should do something about the phosphates. These vital nutrients fuel algae growth. That would explain the rapid decline in chlorine levels. Your test strips are not correct. You are using trichlor and, therefore, zero cyanuric acid is not possible. You want the level to be under 100 PPM. Otherwise, chlorine is less efficient. Even then, there would still be a reading. All test strips are not the same. I suggest that you try using the LaMotte Insta-Test product. With all test strips, take care not to handle with wet fingers and store in a cool, dark and dry place. I hope that this information will help.

I am having a problem keep chlorine in my pool. This problem happened once before and I was told the cyanuric acid level was high. We drained the pool about 2/3 and started to use unstabilized chlorine tablets in our feeder. This corrected the problem. The new problem I encountered was that the unstabilized chlorine tablets turn to mush in the feeder. I can only put one in at a time or it clogs the feeder. I started using stabilized chlorine again and my acid level is back up. Do you have any suggestions on how to keep chlorine in my pool with out using the unstabilized chlorine tablets. (a floater is not an option with my pool type) I have a fiberglass 6000 gallon pool and live in the Florida Keys where the sun is very intense. Thank you.

High levels of cyanuric acid does not prevent you from maintaining a chlorine level. However, levels over 150 PPM can make chlorine less effective and can be remedied by replacing some of the water. The only product that you can use in an enclosed chlorine feeder are stabilized trichlor tablets. You can't use an unstabilized product, as it will disintegrate, release chlorine too quickly and possibly present an explosive hazard. You are unable to maintain a proper level because the feeder is not releasing chlorine at a fast enough rate to satisfy the needs of the pool. Sometimes, especially during hot weather and periods of heavy bather demand, you may have to supplement the feeder with shock treatments. Always try and keep the feeder relatively full and do not allow all the tablets to dissolve. As long as you use stabilized chlorine, you will have to replace water periodically, in order to lower the CYA level. A much better way to add chlorine would be with a salt chlorine generator. I hope that this information proves helpful.

If my chlorine level stays on the high side would I still need to add stabilizer?

It all depends on what the cyanuric acid level is. In northern areas a 20-40 PPM is suggested. In sunbelt areas, 40-80 PPM is frequently suggested. If your chlorine is staying on the high side, it is because you are adding more chlorine than is necessary for your pool, under current conditions. Level above 150 PPM are considered too high and should be reduced by water replacement. I hope that I have been helpful.

► What Chlorine Stabilizer Does?

I have a new pool surface (aggregate) that is now 4 weeks old. All the startup chemicals were put in but I now have a green pool which is really and I mean really hard to brush off the new surface. I was informed that I had not stabilizer in the pool as of yet so I bought that, with a heavy duty bacteria, algae treatment which I put in last night. I followed all the directions with the amount and brushing, but this morning the walls still have quite a bit on them. Is the stabilizer that important, even to have in with the algae reducer? Thanks.

Bruce C., 4/4/2007

Stabilizer helps make the chlorine last longer and that makes it important. Unless you get the free chlorine level elevated, you will not solve the problem. Algaecides and stabilizer are not enough. I suggest that you add the liquid chlorine or quick dissolving shock, about a pound/gallon per 5,000 gallons, until the free chlorine level is over 5 PPM. Don't drag it out! The longer it takes, the more product will be required. Keep it there until the problem is under control. You have green water because the sanitizer level was inadequate and algae took hold. Check the overall water chemistry as well, as it can be affected by the new finish. Have the water tested for phosphates and nitrates, as their presence could promote algae growth and increase chlorine usage. Make sure that you are testing for FREE CHLORINE. A product, such as the LaMotte Insta-Test Strips, provides the right kind of information and is ideal for this purpose. I hope this explanation is helpful.

Sincerely. Alan Schuster, 4/5/2007

I have a very high stabilizer level and have been told that I must replace 3/4 of the water. Otherwise the chlorine will be less effective. A friend of mine, who used to have a pool, said that adding hydrochloric acid will lower the level without any draining. How come the dealer didn't suggest that? Thank you for your time.

Very high levels of stabilizer (over 150 PPM) can reduce the effectiveness of chlorine. The dealer did not suggest that you add hydrochloric acid (muriatic acid), as a means of lowering the stabilizer level, because it will not work! Your friend is mistaken! All it will do is drop the pH and TA and add to the cost and increase the work to be done. The only way to lower the stabilizer level is to replace water. There is no practical chemicals means of lowering cyanuric acid levels! I hope that I set the record straight.

A question concerning Chlorine and Cyanuric acid. Many pool maintainers here use large doses of chlorine to solve any and all problems. They come to us when they experience difficulties. We have recently measured very high levels of Cyanuric acid in a number of pools, in excess of 600ppm. The question is about measurement of chlorine levels in the presence of a high level of cyanuric acid, (over 200ppm). As the acid locks the chlorine in, can the chlorine measurement we take be reliable? We have photometric and titration systems. Yours sincerely,

Paul C., 2/15/2006

Chlorine doesn't solve everything, as you know. Adding stabilized shock can make a bad situation worse. It is not necessarily a case of extreme high levels of CYA interfering with the test results - the high CYA levels will interfere with the action of chlorine and make it necessary to maintain higher than normal levels. As the CYA increases, chlorine becomes less effective. Unfortunately, the pool owner does not take this into consideration. At 600 PPM, there is no doubt that the level needs to be lowered. This can only be done by a major water replacement. I would guess that the pool is in the southwest or Florida and that trichlor has been used for a long time. In addition, dichlor may have been used a shock. My belief is that if trichlor is used, dichlor should never be used. Instead, calcium or lithium hypochlorites, liquid chlorine or potassium monopersulfate should be used as a shock or to supplement the trichlor during peak bathing periods. I hope that I have been helpful.

On opening my 26000 gal. in-ground vinyl lined pool the water tested 130 ppm of cyanuric acid, 390 ppm calcium hardness, scaling/saturation index 0.40, alkalinity 170. I have an automatic chlorinator, mineral sanitizer, a cartridge filter and heater. What procedures should I follow to get rid of this problem? What problems will be caused by this? Our pool store recommended draining half the pool. But, since we can't afford to buy that much water we are taking it down a little at a time and adding fresh water at about four inches down and four inches up. How many times do we need to do this? How low does the cyanuric level have to be before we can start using our chlorinator, mineral purifier and heater? Thank you for your time.

High cyanuric acid levels just make the chlorine less effective and, in turn, requires that higher levels be maintained. You can use everything right now. Replacing 4 inches at a time, means about a 5% reduction. You'll be there forever. I suggest doing it about 12 inches below the skimmer, at a time. In the long run, you will require less water to get the level down. Try and get the level under 100 PPM. Do not use dichlor, as a shock, as it will only cause the CYA level to rise quicker. The fact that you are using a Mineral Sanitizer is helpful, as it allows you to use less chlorine and to maintain a lower free chlorine level. I hope that I have been helpful.

I'm having an inground pool installed with a salt chlorinator. The dealer recommended that I use chlorine stabilizer to reduce the workload on the salt chlorinator. Is this a good idea? Is it effective? Is it a recommended practice? Could it in anyway interact with the chlorinator in a wrong way? Thanks in advance,

Marc, Quebec, Canada, 5/11/2006,

Yes!!! Yes!!! Yes!!! No!!!

If you don't add 40-60 PPM, the salt chlorine generator will have to produce more chlorine and that will shorten the life of the cell. Add it! I hope that this information proves helpful and enjoy the pool.

Sincerely. Alan Schuster, 5/11/2006

Most of what dissolves in a pool remains forever or until you replace the water. Would you rather add it unnecessarily every month? There is no alternative. If you don't add it, the chlorine will dissipate quicker and that will result in having to make the salt chlorine generator produce more chlorine. That in turn, causes the pH to rise faster and it will require a new cell on an accelerated basis. Add the chemical. You only need about 50 PPM. Most pools, using stabilized chlorine, end up with much higher amounts. I hope this information is helpful.

We have a round 27 foot by 52 inch above ground pool. The pH, Chlorine and total alkalinity are all in the expectable range. The Calcium hardiness is a little low (we are treating for that). And the water crystal clear. Problem is our Cyanuric acid is out of control and continues to flux between 111 and the current 127 ppm. We use an in-line chlorinator with one tablet of stabilized chlorine. We have not added anything other than pH decreaser and the stabilizer chlorine tables. We have replaced at least half the water and continue to replace water as needed. My question is what the heck are we doing wrong? This Cyanuric acid thing is driving us up the wall. Regards.

Don G, 8/22/2006

The level is not out of control and you are not doing anything wrong. Those stabilized tablets contain cyanuric acid and, as they dissolve, the level rises. By supplementing the chlorine with another sanitizer the level of increase can be slowed down. By adding a Frog Mineral Sanitizer, you will be able to get the same good results with only having to maintain 0.5 - 1.5 PPM of free chlorine. The chlorine usage will drop, the cyanuric acid rise will slow and the water will look, feel and smell better. I hope that this information is helpful.

I live in the southeast US and have a new gunite pool. I cannot seem to get my stabilizer level above 30. I add the recommended amount of stabilizer, and when I test a week later, it’s still 30 and I have had it confirmed at a pool supply store. What gives? Thanks.

If you are using a stabilized chlorine, the 30 PPM is enough. The use of stabilized chlorine will cause it to rise over time. If you have added stabilizer, on more than one occasion, to get it to a higher level, there is no simple explanation for the problem. I am sure there is nothing wrong with the product. I have been seeing this happen, a few times a year, for the past 30 years. As far as I am concerned, it is a testing problem. I have seen it happen with various brands and testers. This test is evidently capable of being interfered with by trace minerals in the water. Something in your water is preventing a true reading. You have added the product, so just assume that it is adequate and do not add more, as too much will reduce the effectiveness of chlorine. I have never seen a satisfactory explanation for this phenomenon and it evidently is not important enough to warrant a research effort. I know that this is not the answer you expected, but I hope that you will accept this meager explanation and not waste money on further purchases. Enjoy the pool. It is stabilized.

I have been in the pool/spa business for about 4 years and have become a little confused about the relationship between conditioner (cyanuric acid) and total alkalinity. The more sophisticated chemical testing software programs we use to analysis water all make a 30% adjustment for cyanuric acid, in the total alkalinity readings. But, few if any body every talks about it on the many informational web sites out there, including yours. Can you give me a detailed understanding of this relationship, and if it should really be taken into consideration when testing for TA?

Good question!!! The total alkalinity test measures the presence of all materials, dissolved in the water, that are more alkaline than a pH of approximately 4.5. In swimming pool water this includes not only the carbonates and bicarbonates, but silicates, phosphates and cyanurates as well. Cyanuric acid is a weak acid and in swimming pool water forms various cyanurates, which are weakly alkaline. Typically, other than the carbonates and bicarbonates, only the cyanurates are present in a high concentration. Chlorides and sulfates do not have a significant effect upon the pH or TA. Inasmuch as the TA test picks up all of the alkaline materials, it does not distinguish between carbonates/bicarbonates and cyanurates. The purpose, of the carbonates and bicarbonates, is to create a buffer that will help stabilize the pH in the 7.2-7.8 range and they are ideally suited for this purpose. Cyanurates, on the other hand, will register on the TA test, but are not chemically well-suited to act as a pH buffer in the 7.2-7.8 range. High levels of cyanuric acid will inflate the true carbonate/bicarbonate total alkalinity test readings and, perhaps, give a false impression of properly buffered water. To eliminate this error, 30% of the cyanuric acid reading should be deducted from the total alkalinity reading, in order to approximate the true carbonate/bicarbonate alkalinity. The important thing is to consider the ability of the pool to maintain a stable pH, without the need for frequent pH adjustment. In hard water situations and in areas with high TDS, it may be preferable to keep a lower carbonate/bicarbonate TA because of the possibility of scaling and cloudy water conditions. I hope that I was able to explain the theory behind the chemistry.

The level of chlorine stabilizer, in my pool, has been rising all season, even though I haven't added any more stabilizer. Why is this happening?

Every time you add stabilized chlorine, in any form to the pool, you contribute stabilizer to the water. Slowly, over time the level rises and rises. You are probably using a stabilizer chlorine, dichlor or trichlor, for routine sanitizing. To slow down the rate of increase, I suggest that you do not use sodium dichlor as a pool shock, inasmuch as this will only add more to the stabilizer level. There are other shock products to choose from including: liquid chlorine, lithium hypochlorite, calcium hypochlorite and non-chlorine shock. I hope that I've solved the mystery. Enjoy the summer.

I have been using liquid chlorine for sanitizing and as a shock. I know its a pain to lug home those containers and I really don't like the acid, but it is cheaper. If I add chlorine stabilizer will it help? Is it worth doing? Living in Paradise!

Chlorine stabilizer can be used in any outdoor, chlorine-maintained pool. It will help reduce the chlorine consumption and help make the chlorine last longer. That means you will have to lug home fewer containers and have more time to enjoy Paradise. It will help and it is worth it. Have a happy!

First, let me thank you again for the help you provided last spring. Last year and now this I am getting high cyanuric acid level readings (approx. 100 ppm). Last summer I pumped the pool down 12-18 inches and refilled several times with some minor improvement; looks like the same routine this year. My question is, would it be a good idea to use unstabilized chlorine until I get this back to a normal level? Is there a better way to drop the cyanuric acid level other than water replacement? Thanks in advance for your help.

Water replacement is the only way to lower the stabilizer level. You can use an unstabilized chlorine and it will benefit from the stabilizer already present in the water. You may have to give up some convenience. You might continue using trichlor or dichlor at a lower level, by using a non-stabilized shock to supplement the chlorine readings. You will be using less stabilized product and have a slower rate of buildup. Or you might consider a salt chlorine generator! You will give this product some thought, sooner or later, as standard chlorine treatment is declining. Have fun and enjoy the season.

Question: How can I get rid of Cyanuric Acid? I have a 24 foot round above ground pool. We recently drained half the pool and added 6,000 gallons of fresh water. We are currently using a non chlorine chemical as directed. We have backwashed and vacuumed in addition to a lot of other procedures we were instructed to do and we still cannot seem to get clear water. PLEASE HELP! Any suggestions would be greatly appreciated. Have a beautiful day.

Evidently, you are associating cloudy water with the presence of cyanuric acid. There seems to be no basis for this. High cyanuric acid levels can reduce chlorine efficiency, but is not directly linked to water clarity issues. Most likely the cloudy water is due to inadequate sanitizer levels, a filter problem or high calcium hardness. Having drained 1/2 of the water, the cyanuric acid is probably a non-issue, even if your pool is being maintained on chlorine. The only means of lowering the level is to replace water and this has been done. You should have the water tested and get back with more specific details, otherwise, it is difficult to offer assistance on the cloudy water problem.

I am not 100% sure that such a product exists, although I think it has been tried. The problem is that cyanuric acid has limited solubility. Any solution would be fairly dilute and, considering the quantity usually required, would not be an efficient or cost-effective way of adding it to your pool. The best way to add cyanuric acid to the pool is to broadcast it across the surface. It can take a day or so to dissolve, depending upon the pH and water temperature. You may be able sprinkle it into the skimmers, over a period of an hour or so. Make sure that it is done slowly, so as not to clog up the system. I hope that I have been helpful.

My pool supply store told me to add stabilizer. They suggested I wait for a 48 hour period without rain to add. Why? Thank you.

All I can think of it that you misunderstood their instructions. I have never heard of that recommendation before, nor, can I account for any reason for the practice. Most commonly, the chemical is broadcast across the surface. It is slowly soluble and can take a day or so to completely dissolve, depending upon water temperature and circulation. Weather has no bearing! Enjoy the pool season.