Algae Returns Overnight While Shocking...Weird?


Jun 6, 2009
Concord NC
Our pump motor burned out a couple of weeks ago. We got the new one hooked up and running Friday evening, dumped some bleach in and started shocking yesterday am. The pool went 10 days without running, but the water was still crystal clear and the algae wasn't really that bad - just along the usual places - deep end, liner seams etc. The FC held pretty good all day yesterday once we got it up there so we did our last test at 9:30 pm in prep for the overnight test. Well, I wasn't surprised that it dropped 2 points overnight. I was however surprised to see light algae growth back this am in the spots where it was heaviest yesterday. Is that normal? We vacuumed and brushed really well yesterday morning.

Our CYA is 25 so we've been aiming for FC of 12. It was 12 at 9:30 last night and 10 at 6:30 this am. CC was barely .05 this morning. Anyway, we'll be shocking all day today but were really hoping to swim today! :(



Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
Houston, Texas
Keep the pump running 24/7 while shocking. The dead algae will drop out and accumulate along seams and low spots in the floor. You will see it there until all the dead algae is vacuumed or filtered out. Brush and vacuum daily until the shock process is complete.

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
SouthWest Alabama
BY the FC dropping overnight it means that algaae is still growing and consuming chlorine so it's not surprising that it would accumulate in the morning. You just need to keep your shock at 12ppm as often as you can. While I won't tell you you should swim, I will tell you that you can swim up to shock level for your CYA.

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