CYA Testing and Depletion

[Sherra]

If you are worried about damaging the vinyl liner you could use a very large plastic sheet (the clear drop cloth kind you can pick up at any hardware store). You'll probably have to duct tape a few together to get the size you'd need to cover your pool surface plus 5-10 feet on all sides. That would act as a membrane between the old water and the new water and you could do a 100% water replacement without your pool ever actually being emptied.

Splash out/backwashing/etc. will lower your CYA...but not enough to make any kind of difference at all in your number.

[BBB's]

Thanks all for the replies. The next thing on my list is actually Ben's kit. I was in the decision of it and and automatic cleaner and the hold up times on the test kit actually made me opt for the cleaner first. Just wanted to make sure before i do the drain down though. Does the sun have any effect on CYA level in a pool. I have had to keep the pool full with the hose for awhile now since we have had no rain. I was just thinking if it would lower little by little that way that i would just deal with it like that cause my #'s really are not out of the park. Just run the FC level a little higher around 6-8 ppm.

[Sherra]

No, the sun does not deplete CYA. The only way to lower is drain/fill or let your pool turn into a swamp over the winter...and even for some people the swamp thing doesn't change their CYA levels...CYA is a strange creature...

Oh, there is a chemical you can add to reduce the CYA, but it's very expensive and it takes a lot to do it...it's way cheaper to drain/fill.

[CUTURHAIR]

Luckily, my pool's cya drops over the winter and the pool is crystal clear and not nasty. I haven't "closed/winterized" my pool for the last 2 winters and luckily, have not had any problems, knock on wood. However, I have been battling a very small amt of mustard algae this season for the first time, but my CYA seems to go to zero over the winter every year, whether I open to a clear pool, or keep it open and clear all year. I had it tested for nitrates which I believe Ben said could cause that drop, but there were no nitrates, according to the pool store. I believe that test was sent out for testing, and not done at the store, but that was a good few years ago.
John

[CarlD]

OK, let's clear up a misconception:
You CAN dump half the water in your vinyl pool safely. You just need to make sure there's at least 1 foot of water in the shallowest area, then refill. You don't need the Poconos Plastic Sheet method for that.

A CYA of 50ppm is the high end of normal, but still normal--and a good number for a VERY hot,sunny area and lots of usage. That's where you get to if your CYA is 100 and you replace half your water.

Hope that helps.