CYA levels

[TimS]

I've seen repeated posts here stating that the only practical way to decrease CYA is to replace some of the water in the pool. However,
(From Turning Your Green Swamp Back into a Sparkling Oasis)

Second, you need to know your CYA level. If you just got back from vacation you should know what the CYA level was before you left. If the pool has been closed over the winter (or longer), the CYA may have vanished over the winter and you will need to test it.

So does CYA slowly diminish over time? My CYA when I closed was at 70. According to the Pool Calculator, I would need to replace 43% of the water to get from 70 to 40. I didn't drain nearly that much from the pool, and don't really want to replace that much of it in the spring. Is it likely that the CYA level will drop somewhat over winter with the pool closed? Note that the pool has a black, solid winter cover over it, as opposed to a mesh leaf catcher, so there's no direct sunlight on the water all winter.

TIA

 

[duraleigh]

So does CYA slowly diminish over time?

Not left on it's own. However, splashout, rainwater, etc. usually reduce it somewhat over a period of time.

When it vanishes over the winter, it is apparently the result of bacteria getting into the pool that consumes it completely. That bacteria seldom occurs on a properly closed pool so you will probably have CYA next Spring very close to what you have now.

 

[TimS]

Thank you. Hopefully I'll be able to slowly get it down to the recommended level without having to drain too much more. (With the rain we've had over the past 24 hours, it's too bad I have a cover over it. I could have diluted it quite a bit by now.)