Pool Drainage due to high levels of CYA. Water table & drain questions


New member
Apr 30, 2017
San Jose, CA

I'm being forced to drain my pool now because my CYA levels are 300+. I haven't changed the water significantly for 7 years and now I'm dealing with water where I can't kill algae in anymore despite high levels of chlorine. I've read the stories about pools popping out because people don't remove the hydro-static valve and had a few questions to ask in that regard.

First and foremost, I'm wondering if my water table isn't low enough that it doesn't mater to get the valve off. I'm saying this because there's a creek (actually a country drainage creek) behind my house which is as deep as my pool and water is hardly trickling in it at this point. It's hard to imagine that the water table is that high otherwise I would expect it to drain into the creek. Any thoughts about whether or not I may be missing something and it's a bad idea to drain it completely still?

I also got 2 screws off of my main drain in an attempt to remove my hydro-static valve, but for some reason I wasn't able to remove the grate after removing the 2 screws :(. I tried to remove it by prying it with a screwdriver to no avail and I also tried to twist it in case it was screwed in somehow to no avail. My drain looks an awful lot like this one:



Mod Squad
LifeTime Supporter
Jul 10, 2012
Tallahassee, FL
We error on the safe side and say to NOT drain 100% of your pool unless you have a h valve to open. You do need some CYA so.........you can leave some of your water in the pool then refill and sere where you are at.



In The Industry
Jul 8, 2010
Ashford, CT
If you have a concrete / gunite pool I would not worry about it popping up from a drain and refill. There is a lot of weight in concrete... and not a lot of water in San Jose.

You can most likely get away with draining 70% of the pool and refilling.

Also would double and triple test your CYA.

CYA can increase as of the pool chlorine tabs and other pool store powdered chlorine and shock have CYA in them.

As far as your drain cover they just have two screws and otherwise just sit ontop of the drain housing - which both are plastic. ??


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
Why don't you do a partial drain followed by another partial and maybe another (say 50-60% each time) Most water rates make that the safest, most conservative way to drain. Your rates may not make that tenable