High Cyanuric Acid & High Free Chlorine

by Mark

My pool water (15,000 gallons) was a little green and cloudy. I took a reading and found the ppm free chlorine between 5-10. The cyanuric acid runs around 150.

Should I shock the heck out of the pool to combat the green and what will this do to the already high numbers? My ph level is 7.6.

Thanks for the question Mark

As you already know, CYA is the stabilizer for the chlorine. Call it cyanuric acid, stabilizer, conditioner... it's all the same thing.

There needs to be a balance between the chlorine and CYA. The chlorine needs to be 7.5% of your CYA level.

As the CYA rises through Trichlor puck and Dichlor chlorine use, the chlorine must rise as well to meet the CYA demand. Too high or low CYA and the chlorine is rendered pretty much useless. You have a 150ppm CYA. This means to have the chlorine be effective, you'll need to run the chlorine at 11ppm. 11 divided by 7.5% = 146.

This is a huge problem that many pool owners face. They simply want to shock the pool and may not understand the relationship between CYA and chlorine. They also get their information from pool store employees who think they know, but many times don't.

Now, the only way to reduce the CYA is to do a partial drain and refill. Your CYA is up so high that even
if you drain 2/3 of the water and refill, the CYA will still be at the highest acceptable level, 50ppm. If you use Trichlor pucks to dose the pool through the week, the CYA will slowly rise again and you'll be in the same situation.

If you simply shock the pool and possibly clear it up, you're going to be in the same situation you're in right now. The CYA is still too high and eventually the chlorine will be ineffective. You just wasted all that time, money, and chemicals because you're eventually are going to need to do a drain and refill.

Your best bet is to do a full drain and refill, then balance the chemicals out. Test the fill water so you know what the starting point is. You won't get a CYA reading on a newly filled pool so you need to shock the pool with Dichlor. This is a stabilized form of chlorine and will get the CYA in the pool. When you reach the 30 - 50ppm mark, stop and use regular liquid chlorine. You can either use liquid chlorine.

Be careful when using Dichlor as it can get out of hand quickly. For every 10ppm of chlorine added with Dichlor, you'll raise the CYA by 9ppm. For every 10ppm of chlorine added with Trichlor tabs you'll raise the CYA by 6ppm.

Hope this helps and have a great Summer.


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How Much Cyanuric Acid Do I Need?

by Sheri
(Lockhart, TX)

How much cyanuric acid do I need to add to a 26,000 gallon gunite salt pool to raise the level from 45 to 70ppm?

Thanks for the question Sheri

First I would ask you why you want to raise the CYA to 70? Most real pool techs would advise you to keep your CYA between 30 - 50ppm. The range of chlorine for a home pool should be kept between 2 - 4ppm.

I keep the chlorine of the YMCA salt pool, 80,000 gallons with 5,000 swimmers per month, between 3.5 - 4.5ppm. This is the proper range for a commercial pool.

The pool chlorine is 7.5% of your CYA and that range is 30 - 50ppm.

To have your chlorine be effective at a CYA level of 70, you're going to need to run the chlorine between 5 - 6ppm.

Unless you have an extremely heavily used pool for an extended period of time, I would suggest to keep the chlorine and CYA at the levels stated above and this link:

Swimming Pool Chlorine

Pool Chlorine

But if you want to raise your CYA level to 70ppm, this is the rule of thumb:

For every 10 ppm free chlorine added by Trichlor, it raises the cyanuric acid level by 6 ppm. For every 10 ppm free chlorine by Dichlor, it raises the CYA by 9 ppm.

Chlorine Tablets

Pool Chlorine Tablets

Hope this answers your question and have a fun and safe swimming season.


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What Do I Do About Low Stabilizer/CYA In My Pool?

I opened my pool two days ago. My pool size is 22,000 gallons. I added two 1 lb. bags of shock and algaecide. Chlorine tablets were placed in the filter basket.

The pool appears to have a green tint, but the water is clear in appearance. The pH is 6.8, free chlorine was 3 ppm, total alkalinity was 80 ppm, but the stabilzer read 0 ppm.

What should I add?

Thanks for the question

Your chlorine level is good, but if you don't have the right amount of cyanuric acid (CYA)/stabilizer, you'll rapidly lose your chlorine level.

I would first recommend you using Dichlor chlorine initially. This is a fast acting/dissolving chlorine with CYA already in it. Once the CYA is between 30 - 50ppm, use either liquid or granule chlorine. If your fill water is hard, use liquid.

Swimming Pool Chlorine

Chlorine Tablets

The above links have the charts you need to get your CYA and chlorine into the proper range.

Raising the pH level is very simple. All you need is sodium bicarb. Soda ash works very well as does 20 Mule Team Borax. These will raise the pH without much happening to the alkalinity.

Keep the filter running while raising the pH. Use any water features like fountains or slides. This will help burn off the CO2 to raise the pH.

Get a chlorine tablet floater and keep it full of tabs. NEVER put chlorine tabs in the pump basket or skimmer. When the pump turns off, the tablets keep dissolving. When the pump turns back on, your system will get a high dose of acid.

Tab floaters keep a constant flow of CYA and chlorine throughout the week. Normally, a clear emerald green tint after chlorination means possible metals in the water.

You can have your water tested by your local pool store for metal. It's mainly copper and iron that show up. You probably don't have well water, but the above post may apply to you.

If you have a metal problem, this products will help.

*ProTeam's Metal Magic

*Jack's Magic the Pink Stuff (regular)

*Blue Stuff

*Purple Stuff (salt water pools)

These are good metal sequestrants.

The sequestrants that are based on HEDP, phosphonic acid, or phosphonic acid derivatives work the best. Remember that algaecides are used for preventative measures only. They're not meant to clear up a green pool.

If your chemical readings are in line, there shouldn't be any reason to use an algaecide. If you do choose to use algaecide, be sure it's metal and copper free. A good one is called PolyQuat 60.

Hope this helps and have a fun and safe swimming season.


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by D. LEE



Thanks for your questions

Cyanuric Acid (CYA) as you know is the stabilizer for the pool chlorine. Most of the time CYA is not used for indoor pools because they are in a controlled environment while outdoor pools are subject to the weather, heat and the sun, dirt, debris, animals, etc...

Indoor pools can use CYA and there shouldn't be any harmful side effects. The YMCA pool where I'm the pool operator doesn't use CYA either.

Really it comes down to two things:

Health of the pool

You can try to use CYA in the indoor pool and it will probably increase the effectiveness of the chlorine, but it might be a wash financially. You'll use less chlorine but need to buy pool tablets for the CYA.

On the other side, say you're only saving a few bucks in chlorine per month, but then you're adding another chemical (stabilizer) into the pool that it might not need it. I would try it for 2 months and see what the outcome is, both financially and for the pool.

First month without CYA. Write down the dollar amount of chlorine used in that month and keep a record of the readings. The 2nd month try it with the CYA. You can use Dichlor to bring up the CYA, then Trichlor tabs to keep it there.

If it's about the same, I'd go without using CYA. Partial sunlight might create a need for CYA, but I would ask how much chlorine do you go through now?

For your 2nd question about chlorine, it depends on the hardness of the water. I'm in Albany, OR so the water here is very soft, about 2ppm. I don't know which part of OR you're in, but if the water is soft, I'd go with Calcium Hypochlorite.

Calcium Hypochlorite..Swimming Pool Chlorine..Chlorine Granules

It's safer, lighter, easier to store and apply.
For hard water, maybe over 150ppm, go with liquid chlorine.

Sodium Hypochlorite..Swimming Pool Chlorine..Water Care

Also get a Taylor Reagent FAS-DPD K-2006 water test kit.

Pool Water Testing Kit..Balance..Chemistry

Hope this clears it up for you


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