No FC loss in one day in colder water with SWG off


Silver Supporter
Apr 6, 2018
Sugar Land, Texas
Just curious if this is common. I have my SWG off (well 1%). I wanted to know my daily FC loss so I could set my SWG accordingly going forward. Yes I realize I can just shut it off soon due to cooler water temp and just use LC. I tested before pump came on today at 8:00 am and got 7.5 ppm. I then tested at 6:00 pm when pump was off and got 7.5 ppm. No loss of FC. Water temp is 68 deg and my CYA is 70. I’m confident of the CYA as tested by tf-100. Anyways just curious with colder water if it is common to lose no FC in day. I plan on doing same tomorrow. I’d also add overcast all day today with sun going in and out.
water is crystal clear as always. CC 0. Ph 7.8, CH 400, TA 80.


Well-known member
Jul 18, 2017
Antelope, CA
I've learned my readings aren't very accurate if the pump isn't running. Chlorine likes to concentrate in pockets. I always test after the pump has been running at least 30 minutes.

But yes, in general chlorine use goes down (a lot for me) as water temp gets colder. Our pool is just about 60-61 degrees now and losing <1 ppm a day. I also have less sun on the pool this time of year too.


LifeTime Supporter
Jul 21, 2014
Sacramento, CA
The water is colder, the days are shorter and the sun angle is lower and may be significantly more shaded. All of those will significantly reduce chlorine loss, especially with a CYA of 70.

Typically in the winter here (no freezing, no closing) before I had a Stenner pump, adding a gallon of chlorine every 2-3 weeks was sufficient to maintain levels, vs a gallon every day or two in the middle of the summer. That was with water temps 40-60.

I wouldn't bother testing every day; once a week may be sufficient this time of year.


LifeTime Supporter
Aug 19, 2014
Pacific NW
Ya just went through this transition here. 3 weeks ago I was using 1 gallon a week to keep up.
Now it's a half gallon per week. Water is under 60F.

Interesting, it seems to coincide with when my lawn stops growing and goes dormant for winter.
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