Trying to maintain FC above .2ppm


New member
Jul 9, 2010
charlotte, nc
I'm having a similar problem & would love to know more details. I've been dumping chlorine into my pool all week trying to maintain FC above .2ppm. I started with lithium shock, then went to bleach. We're having very hot sunny days, water temp is 91 degrees. On Wednesday night, per recommendations from my local pool store, I added 13 lbs. cal-hypo shock. According to the charts in my Taylor test kit book, this would raise FC to well over 30ppm in my 21000 gal pool. Thursday morning, FC was so high it wouldn't register on my Taylor K-2006 (so it was definitely over 20ppm). By Thursday late afternoon, the FC was 10ppm. On Friday late afternoon it was back to .2. Currently using tri-chlor tablets in an auto feeder :( and have a CYA of 90. BUT, the pool is absolutely gorgeous & clear with no signs of algae. Can't figure out what to do next???


TFP Expert
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LifeTime Supporter
May 7, 2007
Silver Spring, MD
Welcome to TFP!

There are a couple of things that might be happening. At extremely high CYA levels, it is fairly easy to have algae that never really gets fully going, yet never goes away either. Alternatively, you might have gotten some fertilizer, or something similar, in the pool.

Your very high CYA level is going to make this more complicated, especially if you continue using trichlor tablets. With CYA at 90, you need to raise FC up to shock level, which is around 30 to 35, and keep it up there until you no longer have any overnight FC loss. It would be simpler if you lowered the CYA level down to something more reasonable, so your shock level is easier to reach.


TFP Expert
LifeTime Supporter
Feb 23, 2008
Denton, TX

I agree with Jason in that you would be best served by lowering your CYA first. If it is truly 90 ppm, a 50% drain and refill should get you around 45 ppm. 45 is an excellent CYA level (unless you are running a salt pool) and it will be much simpler for you to troubleshoot and manage things.

Have you started reading Pool School? There is a link to it in my signature line.


Mod Squad
TFP Expert
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In The Industry
Apr 1, 2007
Sebring, Florida
Welcome to the forum. :lol: Don't mean to "pile on" but I completely agree that your first, best step is to reduce your CYA by partially draining.

Hundreds, if not thousands of people have never looked back once the CYA gets into a manageable range. As Jason and 257 said, EVERYTHING about pool management just seems to be a hassle with the CYA as high as yours.