Chlorine disappearing during the day


Apr 29, 2021
Northeast PA
Pool Size
Liquid Chlorine
Hi! I’ve been doing a SLAM since Monday as we were losing chlorine fast. Been vacuuming / brushing walls/ taking a toothbrush to returns, skimmer, and light. Pool has been clear since starting SLAM. Lost 2 PPM Chlorine overnight last night, we had a ton of rain yesterday and had to empty water from the pool also we had a ridiculous amount of worms because of the rain. That was all cleaned up before checking chlorine last night. So as I said we lost 2 PPM overnight. Checked at 6 am ( CL 21) lost but didn’t have to add chlorine. Checked again at 9 am (CL 17.5), lost 3.5 PPM, added 1 gallon of 10% should’ve raised it by 7.1 should’ve raised it to somewhere around 24.6 ( I knew I wouldn’t be able to get back to it for a few hours) rechecked at 2:15 and it’s 13.5 😔 My CYA level is 50 so I shouldn’t be losing this much during the day. What am I doing wrong or what should I be checking. Haven’t tested anything else since Monday due to the SLAM PH was 7.2 prior to starting. In the past before I learned about TFP I could always “see” the film of the CYA on the top of the pool, not seeing that at all. I’ve rechecked the CYA twice and yes the CYA reagent Is fresh, just got new stuff yesterday. HELP. I’m struggling here!!


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
At SLAM level FC you will lose more during the day, even with a CYA of 50, than you will at Target FC. By going over SLAM level FC, that is very exposed to UV elimination.
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