Does cyanuric break down over winter?...

I realize that cyanuric levels don't drop in summer except by dilution. Is there something about winter conditions that causes it to break down? I drop the pool level for winter below the jets. Pool is usually full by spring. I test cyanuric a few days after I open the pool in spring and pump has run for a while. I get a reading of zero(couple of kits to doublecheck and also testing at pool store) so I add enough stabilizer to bring it up to 30 or so and don't test again until mid-summer. When I test at midsummer though the readings are high 60-70. I do not use stabilized chorine in the pool, neither dichlor nor trichlor(have a chlorinator, but haven't filled it for last few years). I tend to have green algae bloom problems when the water warms up by july.

I'm beginning to wonder if I am testing cyanuric too soon in the spring. Perhaps it doesn't break down over winter? Perhaps the spring rain water has not been mixed thoroughly enough with the remains of the previous year and I'm being mislead into believing I need stabilizer and therefore regularly overdosing in spring?

When you add CYA in the Spring, I would wait a few days and possibly more like a week before you test for it. It takes that long to get an accurate reading. Could you have been testing too soon after you add?

Secondly, It seems some pools drop CYA over the winter and others will maintain it.

Last, If you have algae...you need chlorine. Post some current test results and folks here will help send that algae to an early grave.

Another possibility is that some kits recommend the water be above 70 degrees for testing. When opening in spring, it is very likely that the water is quite cold. If the water is too cold, fill a bottle and bring it in the house until it warms up a bit and then test.

CYA can be biodegraded in a closed pool by anerobic bacteria. The bacteria will eat the CYA and excrete ammonia and urea. When you open the pool the CYA level has dropped and the pool seems to have an instatiable chlorine demand! It takes a lot of chlorine to burn up all the ammonia compounds before the free chlorine starts holding.

Also, it is very true that testing for CYA when the water is cold can give you a false low reading (as can testing when the water is too hot). LaMotte recommends that their CYA test be done on water between 70-80 degrees. Don't know if Taylor Technoligies has any specific recommendation but since their test is also based on melamine precipitation I would assume the same applies.

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Originally Posted by waterbear

When you open the pool the CYA level has dropped and the pool seems to have an instatiable chlorine demand! It takes a lot of chlorine to burn up all the ammonia compounds before the free chlorine starts holding.

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This is not always true. I always lose my cya over the winter, but never have this 'insatiable chlorine demand.'

Thanks to everyone for the replies.

" Could you have been testing too soon after you add?"

That's possible. I am very careful to only add enough stabilizer to bump it up by 30-35 ppm at most, so either the recommended dosage charts are very inaccurate or I am starting with quite a bit more cya than I think I am in the spring when I open the pool, unless the pool store is adding stabilizer to their 10-12% sodium hypochlorite, which wouldn't make sense as it would only decrease their profits.

I didn't know the tests were that strongly affected by temperature. I will take the advice about letting samples rise in temperature in the spring.

Next year I am not going to add any cyanuric unless I seem to be going through chlorine at an absurd rate and then I'm only going to bump it by 10ppm or so and wait to see what happens in late june/july. Even if I use more chlorine, it will still be cheaper than having to go through problems in mid summer. I got myself off of nature2 and the isocyanurates a number of years ago so I wouldn't have to go through this bs.

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Originally Posted by Watermom

This is not always true. I always lose my cya over the winter, but never have this 'insatiable chlorine demand.'

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You are right...if the anerobic denitrification proceeds to endpoint it will produce nitrogen gas that will leave the water. Conditions for this just don't always happen in a pool so consider yourself lucky. It would be interesting to know exactly what your closing procedure is.