Chlorine loss with auto cover


Well-known member
Sep 28, 2020
Chicago (West Suburbs), IL
Pool Size
Liquid Chlorine
Hi all. Just curious , what causes chlorine loss when my pool is covered with an auto cover? In a 24 hour period my pool lost 1.5ppm. I know it’s not much but I know it talks about here organics and sunlight cause chlorine loss. When there is no sunlight directly hitting the pool what causes that loss?


Gold Supporter
Jul 18, 2018
Canfield ohio
I think you are fine. That is about what I lose over a 24 hour period with my auto cover. Some days a little more some days a little less. If you had algae you would losing much more. Earlier in the year I let my FC get below the minimum and immediately brought it back up to 8 ppm with liquid bleach I keep on hand. I started losing almost 4 ppm per day. I knew I had something then. I slammed for one day and things went back to normal.


Silver Supporter
In The Industry
Aug 15, 2017
Spring Valley, NY
That's pretty much normal and if you think about it it's nothing in the overall picture. It's pretty much impossible to have zero in the water for the chlorine to chew on. 1.5 means there was a minute need for SANITIZATION. Remember the underside of the auto cover could have stuff on it from when it was rolled in the open pool position.


Gold Supporter
TFP Guide
Jun 16, 2019
Hey DIY !!!

Anytime you suspect anything growing you Overnight Chlorine Loss Test. Like in this instance you are wondering if 1.5 Floss is normal with your cover on.

if you pass then it is and you keep that knowledge going forward. If you fail then it isn’t. But when you pass you have all the time on the world to ponder it further because you all but out algae.

Are you verifying you reached your target after adding chlorine ? You could be falling a bit short and not realizing it until tomorrow, looking like more of a loss than it is.

crimson avenger

Gold Supporter
Jun 22, 2019
Salt Water Generator
SWG Type
Pentair Intellichlor IC-20
1.5 ppm is what I lose in a 24 hour period with my auto cover on.
If you divide by 3, that’s about 0.5 ppm per 8 hours. Which is far less than the 1 ppm in 8 hours you’d get for an OCLT.
You are good.


Gold Supporter
Jun 10, 2020
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
That is about what I see when I have the pool covered. I actually have my SWCG turn off when the pool is covered with the auto cover because the demand is much lower. It was a little bit of trial and error to find the right percentage setting on it since it is zero when covered, then x% demand during the day when it is uncovered but a small loss like that over 24 hours does not seem like much at all.

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