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We have an indoor pool subject only to indirect sunlight. What level of CYA (cyanuric acid) then is needed to stabilize chlorine in this protected pool environment. Are there any data which speaks to this circumstance? Would it be advisable to just follow guidelines for outdoor pools in direct sunlight?

Stabilizer is not needed when the pool is not exposed to direct sunlight. In fact, stabilizer is only useful when used properly on outdoor pools.

The stabilizer is cyanuric acid (CYA), which will inhibit the activity of the chlorine on any pool, although on some outdoor pools the sunlight may dissipate the chlorine quickly enough the CYA is necessary to keep any chlorine in the pool.

CYA also does not dissipate, and will stay in the pool until the water is drained. This is where most of the improper use occurs as some products add CYA to the pool as the chlorine is added. The CYA levels reach such high levels that for practical purposes the chlorine all but ceases to work.

Be careful that you are not using a "stabilized" chlorine product to add chlorine to your pool.

Steve Keifer

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Steve Keifer

Thanks for this advise.

Please disregard the statement "CYA levels reach such high levels that for practical purposes the chlorine all but ceases to work."

This is not true. It perpetuates the "chlorine lock" myth. If the CYA really did lock up all the chlorine then it would not be measured as Free chlorine by your test kit - it would show up as combined chlorine.

However, spending money for a chemical that does no better at 100 ppm than 30 ppm is a waste. In an outdoor pool, you need 10 ppm for each 1 ppm of chlorine in the water. So if the max amount of chlorine you plan to have in your water is 3.0 ppm then you will need 30 ppm of CYA. Having 100 ppm of CYA in the water with 3.0 ppm chlorine does not provide any additional benefit. It also does not lock up all your chlorine.

The people that believe that CYA locks up chlorine all point to ORP readings as proof. The fact is that the ORP probe is giving a false reading. When you use a test kit, all the chlorine shows up as free chlorine.

C

Some salt manufacturers recommend a level of 60-80 ppm. Not because it is more effective at that level but because there is a slow loss of CYA due to splashing, backwashing or occasionally, leaks.

Since the level needed is between 30-50 ppm (as Robert Lowry postulates) the pool needs to start with a little bit more than optimum to compensate for the slow decline in the CYA level.

Some Chlorine test strips now have a CYA pad on them and the homeowner can monitor it regularly and add CYA as needed if they wish to keep the level at 30 ppm.

Rick Bays

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Rick Bays

Would this advise apply to indoor pools or pools that are indoor but receive only spotty sunlight over the day?

Hi Bob,

What is the downside if the stabilizer level is much higher than needed?

Mike

I will again state there is no reason to use cyanuric acid in an indoor pool, sunlight on it or not. There is virtually no UV light shining on an indoor pool, which is the only thing the stabilizer will protect against.

Again, Despite Bob's comments, CYA inhibits the activity of the chlorine. No, at no point will the chlorine completely lock up, but that is not what I said.

The manufacturers that make and use CYA have shown with their own scientific data that disinfection times will slow down with higher levels of CYA to the point it can take hours instead of seconds to kill bacteria. I know of no manufacturer of stabilized chlorine products that recommends CYA use on indoor pools. In fact I have almost universally heard from manufacturer's representatives that CYA is not appropriate for indoor use.

I have seen indoor pools with high levels of CYA and normal chlorine levels that are full of bacteria, cloudy and smell somewhat like sewage. Their CYA levels got way out o

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Steve Keifer

It appears this discussion got away from your original question. You wanted to know if CYA was needed in an indoor pool.

Let me clear up any confusion regarding CYA use in indoor pools. It is not needed in indoor pools.

In a previous reply I was responding to some information about CYA use that I thought was questionable or confusing.

There is no need and no benefit to using CYA in an indoor pool. And in an outdoor pool there is no need or benefit to having a level any higher than 30 to 50 ppm. This amount will protect up to 5.0 ppm of chlorine.

Bob