Does cyanuric break down over winter?...

[Watermom]

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.

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

[finch]

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.

[waterbear]

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

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.