Drain Pool & Liquid CL but still high CYA


New member
Jul 30, 2007
Inground, Vinyl, 23,000 gallons, pumps run 7X24
Drain 12" from pool and refilled using well water. Home has a well
Shocked with 8 gallons of CL

48 hours later
FC 2.6 CC 0.6 pH 7.5 Alkalinity 192 Hardness 365
Vaccummed algae from bottom

Pool is clearing up, seeing drain, and vac algae of bottom

What is next
1. Shock again
2. Add Liq CL to keep FC and start puks in skimmer

Can't understand why CYA is so high. Stopped using puks before I drained a few days back

The Mermaid Queen

TFP Expert
LifeTime Supporter
Mar 28, 2007
Northern KY
what is your CYA level? I don't see it listed... How long had you been using pucks?
Sometimes a CYA test will read 100 (the highest level on many tests) when the actual value is much higher.


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
12" of water probably would have dropped your CYA in the neighborhood of 10%. Also, the CYA test isn't very accurate at high levels, so if you thought it was 120ppm, it could have been 150ppm, so draining might not give you a reduction. You'd have to drain half the water out of the pool and replace it to get a 50% reduction in your CYA.

If you have algae, you should never let your chlorine get down to 2.6ppm. You have to keep a constant high chlorine level. No more than 8 hours between tests, and always add what it takes to get back to shock level for your CYA level.


New member
Jul 30, 2007
Thanks for the help. I drain the pool down to the shallow end (just short of the liner) and refilled. Pool mint green (well water).

PH 7.6, FC 0, ALK 270?

CYA better than before but barely reaching the 100 using the Taylor 2006 test kit.

Shocked with Bioguard Burnout 35 (8 lbs) before nightfall.

I will check in the AM.

I will stay away from using pucks. Switch to liq cl and keep it at a high FC.