Disappearing CYA


Well-known member
Jun 7, 2014
St. Bernise, Indiana
I recently moved my above ground pool. I filled the pool with pond water that cleared in a surprisingly fast 24 hour period. I added CYA and waited for it to show up on my test, which it did.

Seven days ago my CYA tested at 30. I use the pool math app, but I must have forgotten to enter the test results. I noticed on Monday last week, my chlorine use was increasing. I was having a rough time getting a proper SLAM done because of time limitations. I figured I was just fighting something unknown. My water is clear and sparkling...I just can't hold chlorine. I had a trip planned for Tuesday to Friday. I knew my pool wouldn't hold chlorine so I added algaecide: Kemtek 60% Algaecide Conc. active ingredient: Poly (oxyethlene (dimeythyliminio) ethylene (dimethyliminio) ethylene dichloride). When I came back, I tried in ernest to complete a SLAM, but I was running out of chlorine and test reagent.

I tested CYA this afternoon and it was 0. I added 4lb. 11 oz to knee high panty hose and hung them by a return.

Is it normal for CYA to disappeared like that? Did the algaecide do it?

Any ideas?

Flying Tivo

Well-known member
Jan 24, 2017
Monterrey, NL, Mexico
With pond water as a fill source you never know what type of organisms are present. Most probably something ate up your CYA and the byproduct is ammonia which also takes some more FC to get killed. You do need to complete your slam.