No FC loss over days


Well-known member
Jun 9, 2014
Marietta, GA
Now that is is fall, and the temps are cooling down a bit, I would guess that FC loss would be lower than in the summer, but is it normal to lose very little if any at all? My water is clear, and all other readings are normal, except maybe my calcium which is 120, but I have a vinyl lined pool. I tested the FC 3 days ago, and it was 6.5 (13 drops), and I just tested again, and it was 6. That is only a .5 drop in over 3 days, is this normal?


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX
You are correct that FC loss slows down as the winter approaches. A .5 drop over three days does seem a little low to me, but it really depends on how much sunlight your pool has been getting and the water temperature.

Since FC can't increase on its own, and assuming no testing errors, I see no reason to do anything but keep testing every few days.

Jim R.


Gold Supporter
Bronze Supporter
TFP Guide
Jul 26, 2016
Monroe, GA
That seems very low. Can measure your water temp? And as said, sunlight is a major factor. I am in same basic area as you, but my temp is about 72-74 because I have been keeping covered, and I get direct sun now from about 8:30-4:00. So I am still running my SWG, although at lower %age.


Platinum Supporter
TFP Guide
Jul 30, 2014
Monmouth County, New Jersey
If you have not added anything to your pool (no chlorine in any form), it has not been used and nothing has fallen in the pool (leaves, etc.), then .5 in 3 days with no cover on is probably due to slight testing error. Was the testing exactly 3 days later? The good news is that, here at TFP, we all now that all the extra "magic potions" that the pool stores sell are really not needed. Take Care!

Numbers ok but water has a hint of cloudiness - Page 6

Please look at post # 114 (Chem Geek) Excellent post on the margin of error when it comes to testing. The whole thread is very interesting.
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