FC not drifting down very fast


Silver Supporter
May 18, 2013
Needham, MA
Second season with my pool. Normally I run a SWCG, but due to low water temps I have yet to turn on. Water is between 57-60 degrees. I opened the pool on April 13. Water was crystal clear, and still had a FC of 2.0 from last fall. The CC was 0.0. Water temp was 44. Laying on the side of caution I brought FC to slam level of 24. CYA is at 60, and for now I am treating it as a non-SWCG pool. Today when I tested my FC is at 14. I have yet to add any bleach since April 13. It has drifted only 10. I do have my solar cover on to catch debree, and to warm the water. Pool gets full sun from 12-5. I know this is a good thing, but can it be a bad thing for the FC to not drift down very fast? I have been testing every other day so I know today was not a bad test.


TFP Guide
Apr 12, 2016
Tucson, AZ
I'd actually say it's a good thing for the FC not to drift down very fast - that means there isn't a lot of nasties in your water for the chlorine to expend itself on.

That said, if you're concerned about having something growing in the water, it's time to perform the OCLT test: Pool School - Perform the Overnight FC Loss Test (OCLT)

If you pass that test, you can continue to let it fall to normal levels for your CYA and use bleach to maintain normal non-SWG levels until you get the water warm enough to fire up the generator.


TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
NW Ohio
Low temperature plus a covered pool makes for very low FC drop, perfectly normal. Like you said, you opened with 2 FC and how many months was that? No reason to worry in the slightest and certainly doesn't call for an OCLT, once your water warms up you will see more normal FC losses. But by then you will be able to turn on the SWG and start getting it dialed in for the season.

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