White Powder On Bottom After Shocking

zdietrich

New member
Mar 9, 2018
2
McKinney
22,000 gallon plaster pool
FC = 5.5
CC = 0
PH = 7.6
TA = 60
CH = 380
CYA = 35
Water Temp = 80 degrees

I'm using Leslie's (I know that's my first problem) Trichlor 3" pucks in a Rainbow 320 chlorinator and typically shock the pool once a week during the summer with Leslie's Calcium Hypochlorite - 70%. The pool seems to stay pretty well balanced except when the FC occasionally drops from me forgetting to keep chlorine pucks in the chlorinator, and then we will get a some yellow algae. I'll use Yellow Out and shock to get rid of that. Other than the occasional Yellow Out, we don't put any other chemicals in the pool. Anyways, every time I shock the pool, I end up with a really fine white powder in the deep end that we have to vacuum out. I though it was DE getting into the pool until I gave up on trouble shooting and replaced the DE filter with a cartridge filter. Apparently DE was not the culprit since I still have the same white powder problem. I've been researching and think it might be calcium from the shock? But my CH levels are on the low end, so not sure if that's it or not. Any thoughts?
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,900
SW Indiana
Welcome to TFP!

The white powder is the cal hypo. Good news is you don’t need it. If you maintain your chlorine according to the FC/CYA Chart You can go years without shocking. Check out Pool School starting with ABCs of Pool Water Chemistry and learn how we take care of our pools with less effort and save money.

I‘m somewhat suspicious of your CYA reading though. The pucks will add that much in just a few weeks, and it isn’t consumed. That’s why we don’t recommend using the pucks except for short term vacations or when you need CYA.
 

zdietrich

New member
Mar 9, 2018
2
McKinney
I will retest the water tonight and verify the CYA. Is the calcium not dissolving into the water because the calcium level is too high? Or is there some other reason it's not dissolving? I would have expected the CH levels to be high.

I don't think it matters, but I've also got a black algae problem that I've been fighting. I got it cleared up (I thought) after I bought the house and got the equipment changed out. But the FC dropped this spring and the black algae came back with a vengeance. I've recently read about treating black algae on here and am starting that process now.