My chlorine level barely moves now...due to cold temps?

Vital Signs

Active member
Jul 27, 2020
Portland OR
So we've considered the pool "closed" for the season due to wet and cold weather (although we haven't lowered the water level or anything....counting on circulation and the occasional heater usage to keep anything from freezing) since Nov 1st. I last added bleach on 11/4/20 bringing the FC level up to just under 6.0 (around 5.8 per pool math). Since then I've testing a handful of times and the FC level is barely moving.

Most recent test on 11/15/20 with tf100
pH = 8.0
FC = 5.0
CC = 0.5
TA = 130
CYA = 30

While we were still in pool season I would find myself adding bleach (1.5 to 2.0ppm's worth) every 3 or so days and bounce between around 3.5 to 6.0.....I'm now on 10 days since my last bleach add and FC has only gone down appx. 1.0ppm.....from 5.8 to 5.0. I've got an auto cover so the water's basically been sunlight free (other then when I'm grabbing a test sample) since 11/2/20. I expected my FC consumption to go down obviously since the pool's not being used but am surprised at just how slowly the water is losing chlorine. Just wanted to see if what I'm experiencing is normal (I'm a new pool owner as of July).....temps over the last couple weeks have been highs in the 45 to 52 range and lows in the 35 to 42 range. Is this only due to the lack of sunlight/usage or is water temp a factor too? I mean, I'm happy if my bleach consumption is going to be this low over the off season but I also want to double check that my testing chemicals are working properly and not giving me false readings....I ordered them in July so I would think they should still be ok.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Yes, lower FC loss is normal as water temperature drops, the sun angle becomes less, and you have shorter days of sunlight and UV.


Silver Supporter
In The Industry
Aug 15, 2017
Spring Valley, NY
You don't have to open the auto cover to grab a water sample. Simply run the filter for 10 minutes and just lift the skimmer cover and get the sample from there.


Silver Supporter
Mar 17, 2019
Chandler, AZ
I'm in AZ and have an uncovered pool, and still haven't seen my FC drop appreciably over the last week, when I turned my SWG off. I really think it's lower sun angle, colder water, and lower usage (in that order). In the PNW I bet you hardly get any UV, plus with a cover you won't get chlorine demand from leaves/debris etc.
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Vital Signs

Active member
Jul 27, 2020
Portland OR
These are all good things to hear....I was thinking I was gonna be adding every 5 to 7 days in the off season but if it's gonna be around 14 days between bleach adds that's even better. Gets real rainy around here in the winter so the less times I gotta mess around with removing my pool cover pumps (my only wall return jet is mid length of the pool) and standing in 40 degree rain to add in bleach the better.


Gold Supporter
Mar 21, 2016
Atlanta Ga
Yea, I am in Ga so not as cold but I barely touch mine all winter. Usually put a couple tablets in a floater and that last all winter
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