Cyanuric Acid in Indoor Pools

[poollady2]

Hi there,
Our pool is indoors, and recently some of our patrons have mentioned that they suffer from itchiness and irritation after prolonged exposure to our water. Our pool is 25ft x 50 ft, approximately 34,000 gallons. We keep the pool at 92 degrees. We use the Prominent Fluid Injection system, a chemical controller that monitors our ORP and our pH. The FC is at 1.5 ppm, and the pH is at 7.5. Our CC is at .5. We use liquid sodium hypochlorite. Our ORP is at is usually about 735. Our TDS is at 1300. We have a high bather load (approximately 120 people per day.) We also do a daily enzyme treatment and an daily backwash to combat the CC caused by our high bather load.

When the pool was put in, the guy who installed it said not to use CYA in the pool, as it is indoors, and not exposed to the sun. Also, the majority of what I have read online, says not to use CYA indoors. Currently, there is no CYA in our pool. However, on a different online pool forum, several people said that I could put 20ppm of CYA in the pool to help buffer our active chlorine. What the people on the forum said was that the irritation was probably caused by the rapid oxidation of the chlorine, and that adding the CYA should help reduce the irritation, as it would lower our active chlorine. (I realize that the CC is also a factor in irritation.) At some point in the future, I would like to add a UV system to our pool, but at this point, we can't afford the $30,000 that it will cost to do so. So... in the mean time, what are your thoughts on adding 20ppm of cyanuric acid to lower our active chlorine, thus combating some of the itching and irritation that our bathers have mentioned?

[chem geek]

This question was asked in this forum and this forum.

Having 4 ppm FC with 20 ppm CYA would be equivalent in active chlorine level to a pool with 0.2 ppm FC and no CYA though at your hotter water temperature it's more like 0.5 ppm FC with no CYA. That would have the chlorine oxidize skin, hair and swimsuits at a slower rate, it would outgas more slowly, and it would lower the rate of metal corrosion. It would also oxidize bather waste more slowly making the use of supplemental oxidation even more important.

However, to handle CC in an indoor pool you really need to have supplemental oxidation such as the UV you mentioned. Enzymes might help as you are using, but some facilities use non-chlorine shock (MPS). UV is generally best, however. Ozone is sometimes used as another alternative though more commonly outdoors.

Also, your pool as a commercial or public pool must follow state and local regulations so check those as some do not allow any CYA in the water for indoor pools.

[poollady]

Thanks chem geek. So if I understand correctly, your suggestion for our current situation is to go ahead and add the cyanuric acid, even though we don't have a UV system, and simply continue using MPS as additional oxidation. With all due respect, have you seen indoor pools using cyanuric acid firsthand, or is this a theory that you believe will work, without causing other problems? Thanks for your feedback.

[chem geek]

We have seen high active chlorine levels be a problem in residential spas and indoor pools, but not your situation in a commercial indoor pool with high bather load, CC, and reports of irritation. You should probably first focus on getting a handle on the CC and see if that addresses the irritation problem. The pool industry does not believe in using CYA in indoor pools because they only consider CYA's effects as protecting breakdown of chlorine from the UV in sunlight and do not consider that CYA significantly moderates chlorine's strength. Some in the industry believe in blasting with high chlorine levels (and high ORP as a result) to oxidize bather waste without consideration to creation of disinfection byproducts or the effects on swimsuits skin or hair (several of the following articles at PPOA talk about not using CYA in indoor pools):

http://ppoa.org/?page_id=57

As I wrote earlier, your state regs may not allow CYA in indoor commercial/public pools. You can look up your regs at this link.

If you add CYA to your pool water, you can only remove it through significant water dilution so it's largely a one-way commitment. As I noted, if you do have some CYA in the water, you need a higher FC level since CYA significantly moderates chlorine's strength. Though the lower active chlorine level may produce some of the most irritating CC (nitrogen trichloride) more slowly, you will definitely need supplemental oxidation to get rid of the bather waste. That is, it might help prevent future problems, but it probably won't fix your current one (i.e. it won't reduce your existing CC).

[USER]

Are you running your system 24/7? with 120 people a day swimming in it, would be a must.
What type of filter do you have? Having to backwash everyday would start to effect a DE or sand filters performance.
How long has this been happening? Since the pool was built? Only a short time?
Have you tested the water yourself using a test kit? Your injection system could be giving wrong reading causing problems.
With that amount of swimmers how often do you replace the water? Have you ever replaced it?