Cyanuric Acid: A Discussion on Chlorine Stabilizer

cyanuric acid chlorine stabilizer

You may know CYA as pool stabilizer or conditioner. This curious chemical seeks out and attaches itself to the chlorine molecule. In doing so, it acts as a sun shield, absorbing sunlight, and reducing the sun’s degradation to your chlorine.

The chemical was discovered in 1829, by Friedrich Wöhler a German chemist. It was not until the 1950s, however, that a class of disinfectants known as chlorinated iso-cyanurates were developed. Soon after, savvy chlorine manufacturers  began adding it to “stabilize” chlorine tablets.

Cyanuric acid that is sold as pool stabilizer or conditioner is a white, flaky powder, similar in appearance to calcium chloride. It is a weak acid, and is not corrosive or considered hazardous.

How is Cyanuric Acid Used to Swimming Pools?

pool-stabilizer-label

Stabilizer should be added to refilled pools to raise the level to the range of 30-50 ppm. After this foundation, the small amount of CYA pressed into your stabilized tablets should help replace the CYA lost during backwash, splash-out or winterization.

The TriChlor tablets and the DiChlor shock that we sell are examples of chlorine products that are combined crystallized with the salts of cyanuric acid. These are known as stabilized chlorine and are meant to help maintain the residual of cyanuric acid in your pool.

Cyanuric Acid Reduces Chlorine Degradation

I like to think of the CYA molecule holding a sun parasol, shielding the chlorine. While it absorbs up to 50 percent of the sun, you can expect to see a reduction of up to 50 percent of your chlorine usage. After adding CYA to the pool, you’ll immediately notice the increase in your chlorine’s lifespan, and your wallet size.

A pool without stabilizer can lose 90 percent of its free chlorine with just a few hours of bright sun. When stabilized, your chlorine level will last longer, and you’ll use about half of the tablets to maintain your chlorine residual.

Too Much Cyanuric Acid

A 2007 study by the CDC showed that levels of Cyanuric acid above 50 ppm significantly diminished chlorine’s ability to kill bacteria. Chlorine molecules that are overprotected by too much CYA can lead to excess chloramine formation as nitogen and ammonia are easily able to attach themselves to these “slow and sluggish” chlorine molecules.

Many users of chlorinated isocyanurates report problems with a buildup of CYA over time to levels beyond 50 ppm. To lower the levels of CYA, there is no magic potion. Lowering CYA levels is accomplished by dilution; that is, draining and refilling a portion of the pool water.

If you are using stabilized chlorine (Trichlor or Dichlor), and you have problems with too much CYA, without the ability to drain and refill, you can switch chlorine types. Cal Hypo tablets and shock can be used that do not contain cyanurates. Trichlor and Dichlor are a nearly 50 percent cyanurate compound.

Another solution is to switch to a salt water chlorinator. You’ll still want to add CYA to the pool to help your salt cell from working too hard, but you won’t be adding additional CYA from stabilized tablets or shock.

Still another solution is to add a mineral sanitizer like Nature2 or Frog, or add an ozone purifier from Del Ozone to reduce your chlorine demand by half, which will reduce CYA buildup by also exactly half.

To lower the CYA level by dilution, here’s the math. If your cyanuric acid level was at 100 ppm (way too high), and you want to lower it to 50 ppm, you will need to replace half the pool water (assuming your fill water has 0 ppm of CYA).

Cyanuric Acid Reduces Kill Rates

A study performed by the Pinellas County, Florida, Health Department found that when pools with 1-5 ppm of chlorine were treated with 100 ppm of cyanuric acid, nearly 80 percent of the pools would be deemed unfit for swimming by the sanitarian.

Experts on poolforum and TroubleFreePool such as Richard Falk (chemgeek) and Ben Powell have led lengthy discussions on the topic of the suppressive effect of cyanuric acid on the efficacy of free chlorine levels. Charts have been produced to help pool owners find the best chlorine level, based on their level of cyanuric acid.

In most cases, and with the exception of Crypto or Giardia contaminations, these higher chlorine levels will compensate for the effects of cyanuric acid on chlorine activity. For heavily used commercial pools, it has been suggested that double this amount be used. This would roughly equate to a maintaining chlorine levels at 20 percent of the cyanuric acid level.

Notice also in the chart below that it’s not only the daily chlorine residual that needs to be boosted to compensate for the CYA, but also when shocking the pool. CYA bonds almost instantly to chlorine in the water and makes it difficult to reach breakpoint chlorination.

So, what’s the problem? When the chlorine isn’t as powerful as you think it is, your pool is not as sanitary, and possibly not fully disinfected. The validity of the standard minimum 1.0 ppm free chlorine has come into question.

OK, what’s the answer? If you add pool conditioner or stabilizer, or use Trichlor tablets or Dichlor shock (both stabilized chlorine types), you should make some adjustments.

Ben's Best Guess Chart

1. Run your chlorine level higher. As compensation for the suppressive effect of CYA, use more chlorine tablets until you test a consistent 2 or 3 ppm.

See chart, adapted from Ben’s Best Guess Chart at Pool Solutions, that has some recommendations for chlorine level, at different levels of CYA.

In short, the higher your level of cyanuric acid, the higher your chlorine level.

2. Monitor your cyanuric acid Level. Test your level at the start and end of every season. Don’t add any cyanuric acid to the pool if you already have 20 ppm. Remember that chlorine tablets add cyanuric acid, and the level will increase naturally. If your cyanuric acid level gets too high, dilute it by draining a portion of water and refilling or using Bio-Active CYA reducer. Test your level with a good test kit, like my favorite Taylor K2005, or use Test Strips that check all levels, like LaMotte 6-way test strips.

Not Enough Cyanuric Acid

Outdoor pools without a residual of cyanuric acid in the water have trouble maintaining a chlorine residual during a sunny day. Even small levels of CYA in the water will have a pronounced protective effect.

Indoor pools can also benefit from a very low residual (5-10 ppm) of CYA as it helps to prevent off-gassing of chlorine and reduces chloramine formation.

If you need to raise your cyanuric acid level, you simply pour the granular white powder directly into the pool, at a rate of about 1 pound per 10,000 gallons to raise it about 10 ppm.

The Best Level of Cyanuric Acid

Aquachek-pro-II test strips for Cyanuric Acid, Hardness and TDS

Testing the water for a cyanuric acid level is the first step. The test for cyanuric acid is interesting; it’s called a turbidity test. The presence of CYA will turn the water sample cloudy, or turbid.

If you don’t have a turbidity test for CYA, you can use these test strips to check your cyanuric acid, hardness and total dissolved solids (TDS) levels. Since you only need to check these levels monthly, it makes sense to have separate test strips for these tests.

Maintaining the level around 30-50 ppm is recommended. There is little advantage in exceeding the level, and as shown above, the higher the level, the higher the kill time for your chlorine becomes.

Too Much Cyanuric Acid

Other effects of high cyanuric acid levels include problems with cloudy water, and a difficulty in maintaining a free chlorine level in the pool, with a corresponding increase of chloramines.

in-the-swim-bio-active-cyanuric-acid-reducer

Lower your level of cyanuric acid by dilution (draining and refilling with fresh water), or by using Bio-Active cyanuric acid reducer. You can reduce the amount of cyanuric acid added from chlorine tablets by using a mineral purifier or an ozonator to reduce your chlorine demand by 50 percent.

So students, here ends another lesson in swimming pool chemistry. In summary: It’s prudent and necessary to use some level of cyanuric acid. Test monthly to be sure that it doesn’t rise much above 50 ppm over time, and if it does, lower by dilution, until we come up with a better solution.

Is Cyanuric Acid Dangerous or Unhealthy?

Cyanuric acid by itself is not immediately dangerous or hazardous to one’s health. It can cause eye or skin irritation if direct contact is made. It is not toxic or carcinogenic. Based on data from toxicological investigations, cyanuric acid does not damage organs. Damage to the kidneys and bladder has been observed in rats tested with a saturated solution (5375 ppm) of cyanuric acid for their drinking water. CYA should not pose a risk to humans during  use in swimming pools. Cyanuric acid is quickly excreted unchanged from the kidneys.

Can I Use Cyanuric Acid to Lower my pH?

Technically, CYA is an acid and is in the family of sulfuric acid, with a pH level of around 4.0. It will slightly reduce your pH level when added to the pool in measureable quantities but may be hard to notice. So, no, cyanuric acid is best used for shielding your expensive chlorine from the sun, but for lowering your pH, better to use sodium bisulfate.

50 thoughts on “Cyanuric Acid: A Discussion on Chlorine Stabilizer

  1. I just purchased a home with above ground pool, approximately 5,000 gallons. My CYA is a little low on the test strips, what should I add to it? I am new to pool ownership, other than shock and chlorine tabs, what other chemicals should I have on hand to add as needed. Also, my chlorine tabs in the floater are very slow to dissolve but chlorine levels are good. How long does it take for them to fully dissolve? Does cooler weather also affect dissolve rate? Thank you!

    • Hi Kristi, CYA, aka stabilizer, protects chlorine from the sun. If you don’t have heavy sun or problems maintaining chlorine levels during the hottest part of the day, you can safely ignore this measure. The tablets are stabilized, and add a small amount anyway, with each tablet added. Tabs do dissolve more slowly in colder water. The other main level to watch closely is pH, and if you are having pH problems, look at alkalinity closely. If your pool filter is on the small side, it can be helpful to add a weekly dose of Clarifier and Algaecide to the pool, per label, probably just 1-2 oz each, per week.

  2. Confused Chemist

    Hi, all readings good, chlorines, alkalinity and PH. But cyanuric acid is registering a zero. Currently have foggy water. Will a stabalizer/conditioner clear this? Can’t see it will if chlorine level is where it needs to be? Any suggestions?

    • Hi, stabilizer protects chlorine from the sun, but does nothing for water clarity. Look to your filter, either it is not operating correctly, or being run long enough. During the hottest part of the summer, pools need several more hours of filtration time, perhaps 50% more than during spring or fall. A Clarifier can help also with the cloudy water.

  3. I have basically zero on my test for CYA but im using stabilizer chlorine tablets I notice this year as its first time using these chlorine tablets that my tablets are lasting way longer then ever before one 3 inch tablet will last over a week with many sunny days my pool is in direct sun no trees at all and gets sun at min 10 hours a day. Im not going to adjust my CYA because I feel these tablets will raise it in time on there own is this correct or should I add some to raise CYA??

    • Hi Todd, no need to add it if the tablets themselves are working. Since you are using stabilized tablets, the chlorine or hypochlorous acid as it gets wet, must already be bonded well to the cyanurates, protecting them from the sun.

  4. I’m just opening my pool for the year, not later than normal but it’s no longer green just cloudy. I had my water tested by the local pool store as well testing myself and my stabilizer is low. I’ve added liquid stabilizer to my pool as instructed by my local pool store but and still unable to get a reading in a normal range. It’s still saying low. So I’m not sure what I need to do? How can I get my stabilizer up? Do I need to add a lot of shock since my chlorine is low and my free chlorine is 0?

    • Hi Ashley, it usually takes a few days for the CYA additions to start to test… not sure why? But give it 3-5 days. If your chlorine is low, or 0, it is urgent that you get chlorine level up fast, with shock chlorine, to clear up cloudy water, start with low pH, high chlorine, 24/7 filtering, and Clarifier. If it still does not clear, investigate the filter, is water possibly bypassing? Is the filter media tired or worn out? Have you cleaned the filter really well lately, with a Filter Cleaner, or other method?

      • I just had the sand in my filter replaced this year. The maintenance guy didn’t say anything was wrong with the filter itself. I backwashed my filter prior to adding the stabilizer to ensure it was good and clean since I couldn’t backwash for 3 days after adding stabilizer. I do run my filter 24/7, I’ll add chlorine tonight. Should I add more than the required amount of shock for my 24 ft round pool?

  5. I have a 30,000 gallon pool. Upon returning from a weekend away, we found our pool to be cloudy (all was good before we left). For the last 10 days we have not been able to get much of a free chlorine reading.(0 to 0.5) Total chlorine is around 1 . PH was low and we raised it to 7.2 but it doesn’t want to stay there, falls to 6.8. Hardness, and alkalinity are great. Cyanuric acid is at a 0. We have had two pool places tell us different things and said our numbers looked ok. We have done everything, even replaced a 1/4 of the pool water. The pool is clearing slowly but still no chlorine readings. HELP! THANKS

    • Robyn, you should add 9 lbs of cyanuric acid (stabilizer) to have a 30 ppm level of CYA, to protect chlorine from the sun. Then add 9 lbs of shock (yes 9!), and brush the pool, while running the filter overnight. That should rectify things and break thru the chlorine lock problems, kill the chloramines, and restore water clarity.

  6. I went into my pool store to test my water after draining and refilling 60% of the water to get cya levels down. It came back at 5ppm after being at 130ppm. They suggested adding 3 lbs of stabilizer to bring it up. I diluted 16oz of stabilizer, which according to the package should only raise it 10ppm. Went in two days later to test, the result was 73ppm. I raced home to pull the nylon with second does 16 oz before it dissolved. It had dissolved about 3/4 or 12oz. Is it possible for my cya to have shot up 68ppm if I added only 16 oz of stabilizer and no other chemicalS?

    • I suspect that the second test of 5ppm was faulty, because it fails the math test. If you were at 130 ppm, and drained 60% of the water and refilled with fresh water with 0 ppm cya, then the new CYA level should be 60% less than 130ppm, or roughly 55 ppm. The general rule for CYA is, 1 lb of CYA, added to 10,000 gals water, will add 10 ppm.

  7. Vickie Settle

    In an above ground pool, we don’t usually circulate longer than four hours. Just added stabilizer through the skimmer. Is there a problem with running just 4 hours a day after adding it? I added only half of what the total dose is. Will dose second half tomorrow. Will not be backwashing for 7 days.

    • Hi Vickie, cyanuric acid granules take some time to dissolve fully, but by now they likely are fully dissolved. It does take a day or two, but probably not a full week. It will dissolve in the filter tank, without water running over it. But why (?!?) run the filter only 4-hrs per day? Pool water that is over-filtered has more resistance to algae and bacteria, and uses less sanitizer. Pool water that is under-filtered is susceptible to lots of problems in water quality, problems that cost money in chemicals to correct, and creates a higher chlorine demand. Most filter systems are configured in size to turnover all of the pool water in an 8-hr period, or filter all of the water in 8 hours. In 4-hours, only half the water has been filtered, and these contaminants and particles can lead to cloudy water and provide nourishment to algae. Especially as the water warms into summer, I would encourage more filtration 🙂

  8. Do I keep my salt generator on when adding stabilizer

  9. hey dave. what is the re entry time after adding cyanuric acid to the pool? are there any guidlines?

    • Davy Merino

      Hi Scott, I don’t believe there is any wait time, after adding cyanuric acid. If you broadcast it into the pool however, you may want to wait 24 hours or so, to avoid undissolved granules from getting in anyone’s eyes. CYA does create some heat when added to water, part of the reaction to water, but I’ve had my hands in the stuff wet – stirring it in the skimmer, and it never affected my skin. If added to the skimmer, try not to backwash for 24 hours or longer, as it takes a day to fully dissolve.

  10. i have high free chlorine level and high stabilizer level – i have stopped adding chlorine to pool..will the free chlorine level come down..have not put in chlorine pucks for 3 days – still getting high levels – inground pool 12×28

    • Hi John, yes it will come down soon – no worries! High cyanuric acid levels makes chlorine less active, to protect it from the sun, but it gets so lazy that it can fail to kill bacteria and algae. Experts suggest that when cya levels are high, chlorine levels should also be run at a higher level, to ensure healthy swimming water. So whereas 1.0 ppm is standard safe without using cyanuric acid, 3-5 ppm is considered best when stabilizer levels are around 50 ppm, and correspondingly higher, for higher levels of cya.

  11. Marie Jablonski

    My cya is now at 100ppm. The lowest I have gotten this year was down to 70ppm. I have reduced water, added it back numerous times. I am adding granular chlorine as needed. I have use chlorine tabs with stablelizer throughout the winter months. Pool is not cloudy. In fact it’s clear as can be. What do you suggest I do? Thank you

    • Hi Marie, there is a product called Bio-Active that is a cyanuric acid reducer. Claims to remove 50 ppm with one $45 treatment, but results are mixed – seems to work for about half the people that try it. If you do, follow package instructions very closely.

  12. How long after adding CYA to my pool can I add chlorine? I started with a chlorine reading of less than 0.5 ppm. I applied the granular CYA over the surface of the pool as directed on the package. Thanks.

  13. Lisa Sonnenberg

    My cya level is 100 and that’s after draining some of my pool. I checked it today and it’s still 100, but my free chlorine level is at 0 so I’m needing to shock my pool. I have liquid shock but I’m afraid it will raise my cya levels again. What should use? My pool is a 24X52 round pool. This is my first pool and I’m kinda lost. Any help would be greatly appreciated.
    This was my full reading from the water this morning
    Hardness was 250
    Total chlorine 1
    Free chlorine 0
    Ph was 7.2
    Alkalinity 120
    Stabilizer 100

    • Hi Lisa, you can use liquid shock, it contains no stabilizer, cal hypo granular pool shock also has no stabilizer. The only stabilized chlorine are the Trichlor Tablets and Sticks, or DiChlor granular shock (what we call Di-Zap). 100 is too high, and it could cause problems, draining half of the pool and refilling should lower it to 50 ppm, which is at the top end of the normal range of 30-50 ppm. Otherwise your readings look good. So you are safe to shock the pool, or you may choose to lower the water first, then shock as you begin to refill…

  14. I have seen other comments on other forums that you should wait a week or so to test your cya. guess it takes a while for it to show up.

    • Davy Merino

      Hi, it can take a day or two to fully dissolve, but usually is testable the same day that it is added. If adding to the skimmer, be sure not to backwash for a few days. You can also sprinkle it in the pool, and brush a few times to help dissolve, or run the pool sweep

      • I attempted dissolving 2.5lbs of CYA granules in portions in warm water before adding it to the pool.What didn’t dissolve I put in a sock and placed it into a skimmer. The pool is 4 years old and holds 17,000 gallons and read 10-30ppm on a dipstick and was ND using the test tube method after mixing 30ml of H2O & fresh CYA reagent each. I haven’t been able to hold a substantial free chlorine level in the pool since bringing it up to 15ppm initially and everyday since.it’s been 5 days since adding the CYA and the readings remain the same. I believe the CYA should have gone active by now and the free Chlorine should not disappear overnight. The pool is crystal clear and sparkling and all other chemicals are normal. Advice?

        • Hi Rob, sometimes it takes a few days for the cya to register and test, not sure why. Now you’re at 5-days… hmmm. And having trouble with getting a chlorine reading. I would try the ol’ “Triple Shock’ treatment, which usually will break-thru whatever is consuming the chlorine (nitrates?), and allow a good reading to register.

  15. Pamela Kissinger

    I have Saltwater Stabilizer. Is that the same as this CYA stuff discussed?

    • Davy Merino

      Hi Pamela, good question. anything called Stabilizer, or Conditioner, is always going to be using a cyanuric acid base, so yes, same as CYA. thank you.

  16. jim fagan

    Great article. Best explanation I have read. The sun screen analogy is easy to remember Thank you.

  17. my cya level was not registering. It was well below the 30 mark. We added to stabilizer as directed and still the following day we had 0 reading. I had added an additional amt with still 0 reading. We have a salt water pool so today i added 1 gal on chlorine and at least we now have a high reading of chlorine. Is it maybe a bad stabilizer?

    • Davy Merino

      If your chlorine is still high tomorrow, or today – the cyanuric may be in the water. I am suspecting bad test results? Not a common thing, so maybe the reagent is bad, or the test strip. Be careful that you don’t add too much. If you use tablets to sanitize the pool, you only need a few lbs to start (if near zero cyanuric). Using tablets will slowly raise the cya over time, unless you get a lot of rain, or backwash the pool a lot.

  18. François Lachaîne

    What are the health risk of having a high rate of stabilizer. Tried to lower my level that is at 172ppm to 145ppm but it seems to fluctuate upwards eventhough i have stoppep using tablets with stabilizer stricktly using granular chlorine?
    Thanks for your help

    • Hi, there was a study done long ago which hyperdosed lab mice with cyanuric acid, and some had kidney failure. No studies have been done specifically related to pools, to my knowledge. No known health risks. If you cannot pump out some of the water and refill, then repeat… to lower the cyanuric acid, you could try using BioActive as a reducer. Dichlor pool shocks do contain stabilizer, but Cal Hypo or Lithium Hypo shock do not. I would go back to tablets when you can, as using shock is inefficient and creates peaks and valleys of chlorination.

      • I would recommend liquid Chlorine with zero CYA issues. All you need is a small base of CYA in the water 30-50 ppm and it will never go up if you stay away from pucks. I have a liquid off-line liquid Chlorine feeder (HASA Liquidator) works with the pump. I add a couple of gallons a week to the feeder tank (pump speed atleast 2500 rpm mine is 2800 rpm needed for feeder to work properly). Other than that, I add dry acid about once a week to keep PH at 7.4-7.6 (TA is more stable with Liquid Chlorine). Cal-Hypo is load with Calcium so you have another problem similar to CYA build up along with scale issues so not an ideal alternative. The Lithium Hypo (in tablet with feeder) is better choice but more expensive. You can get HASA Liquid Chlorine (18%) in returnable bottles in a case of four about $15.00 from licensed pool stores. I just buy the 10% HASA in a two pack for $9.00 which I recycle the containers. Some people like SWG but when, not if, the cell goes out it costs several hundred dollars to replace and ph has to be watched very closely (not maintenance free). Also have to know what your metal equipment is and if SWG is comparable because salt can be corrosive. My neighbor went from pucks to a SWG and now his pool sits “EMPTY” can’t say for sure what happened but OMG. So make sure you know all the pros and cons first….I think liquid Chlorine is the least problematic and economical.

  19. I have added 3.5lbs of chlorine stabilizer to my 11,000 gallon pool by recommendation from our local pool and spa store because it was reading 0. It has been 3 days since we added this and my total chlorine and free chlorine levels are registering at 5 ppm but my chlorine stabilizer is registering at 0. I’m confused, why is the chlorine stabilizer still reading 0 but the chlorine levels are high?

    • Hi Crystal, 3.5 lbs should have raised the cya to around 30-40 ppm in your pool, and likely did, since your chlorine remains high, which is normal for the initial cya treatment. I would suspect that the cya testing method is incorrect, or the reagent/strip is no longer good.

    • Every year my cyanuric acid levels get higher as the season goes on. If all tablets have CYA in them why don’t they sell tablets without CYA added. I live in New Jersey and have a plastered gunnite pool. Is there CYA in shock? Is the only answer to lower and refill pool. If I do lower and refill it will go high again. Help please.

      • Hi Steve, yes all tablets and sticks are stabilized. Di-Chlor shock is stabilized, but Cal-Hypo and Non-Chlorine shock is not. The solution is dilution as you mention, or a cyanuric acid reducer called Bio-Active, which claims to reduce 50 ppm, but reading the reviews, it’s favored by only about half of those that reviewed it. Other methods to reduce cyanuric are to reduce the amount of tablets used weekly, by installing a Nature2 Express purifier, or ditching tablets altogether and installing a saltwater system. In the first case of Nature2, you can cut tablet use by half – cutting the cya additions by half also – and with a salt system it adds no cya to the water at all, although you will still need it, to prevent the salt cell from overworking, against sunlight degradation. A third way to reduce tablet use is to filter the water longer each day (or filter better with a large DE or Cartridge filter), and use non-stabilized shock more often, say weekly. Algaecides and clarifiers can also help reduce the chlorine demand.

  20. Elaine Mills

    This has happened to my pool three years in a row. When I get my CYA level down to 50 or lower (80 now) and I use bleach instead of shock or tablets will the level of CYA remaining keep the chlorine from dissipating?

    • Hi, bleach does not have any added stabilizer, so it won’t be adding any new cya to the water. The remaining level in the pool will stay in the water to help protect the chlorine from the sun, yes. Bleach is a very high pH (13+), so be sure to check and lower your pH level often, which may cause you to need to raise the alkalinity level, a few times during the season.

      • Robert J Beck

        I have a 22950 gallon above ground pool with a cya reading of 200 liquid chlorine goes fast in it. It seems if i maintain a high chlorine level with added copper alagecide pool seems fine. Any suggestions draining not an option due to drout

        • Hi Robert, I would give BioActive a try – it’s a cyanuric acid reducer. A bit pricey at $45, but can lower cya up to 50 ppm, so you’d need a few bags. But try one at first, following label instructions closely, to determine how much it will reduce the cyanuric levels.

  21. Roy bracken

    With a cya level of 50, would it ever be necessary to add more stabilizer to my pool, since cya levels will not decrease without dilution?

    • Yes, it can for pools that receive a lot of rainfall, or for pools that are winterized using safety covers, for which the pool water level is often lowered 12-18″ when closing. In both cases, when the pool is diluted with enough rain/snow, and the following season may need a cya booster

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