Where did my CYA go


May 27, 2018
Carthage, NY
30,000 gallon pool. When I closed my pool last year I was at 30 CYA. When I opened it this year, the tube was clear. I use the Taylor test kit. My PH is 7.4 to 7.6 and thanks to this site I've figured out how to use the borax to keep the PH where I need it. I slammed the pool when I opened and it cleared up nicely. I added 2 pounds of stabilizer using the sock method and the tube was still clear, 2 more pounds, still clear, 2 more pounds, and its getting cloudy but I'm still seeing the dot while holding it at waist level with my back to the sun at the 30 level. The reagent I bought "expired" last year so I have some new stuff on order but I don't think that's the issue. I'm burning through chlorine much quicker than last year and had an algae bloom last week, which I'm chalking up to not sweeping the pool often enough even though I had the FC up around 4 consistently. I slammed it and after 8 gallons of 12.5% bleach, the pool cleared up in 48 hours.

I've read that you don't lose CYA unless you remove water and replace it. When I opened it, I had to drain some of the water due to all the snow melt. Could the CYA have setteled and been drawn out when I drained about a foot of water out of it? Based on pool math, 6 pounds should have me at 24 if I had fresh water. I have to imagine there should have been some in there from last year. Should I go ahead an add the last 2 pounds I have or wait till the new reagent?

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I've read that you don't lose CYA unless you remove water and replace it.
For the most part that is true, however a small amount is expected to degrade each month - approximately 5 ppm. Plus you had some water exchange. So if you had 30 ppm say last Oct, then opened in Apr, that's your 30 pm. The PoolMath APP shows me it takes about 7 lbs of stabilizer to go from zero to 30 ppm in your 30K pool. So far you've added about 6 lbs, so I think you're getting close and that why it's cloudy in the viewing tube. I would add another 10 ppm worth (40 ounces) which should get you to at least 30 ppm.


Gold Supporter
Jul 8, 2015
I try to maintain about 70 ppm in mine during the pool season.. I don't add any during the winter and come next spring I'll loose half easily.. 30-40ppm.. so that is in line with what you are loosing as well.