Chlorine Loss


Jan 4, 2021
Spring, Texas
Pool Size
Liquid Chlorine
Thanks to this forum and the pool math app I have finally dialed in and balanced my pool water. latest results as follows.
FC 4.0 added 20 oz 10% liquid chlorine to get chlorine to target level of 5.
CC 0
PH 7.5
TA 60
CH 260
CYA 40.
Everything has been going good pool water is looking very clear. My question is how much chlorine is an acceptable loss in a day? I test my water early in the morning every day and it always seems like I am back at 4.0 or 3.8 so I add recommended amount of chlorine that pool math app states to get back to 5. Thanks.


Gold Supporter
Bronze Supporter
Jul 17, 2019
Prosper, TX (DFW)
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Seems reasonable, but it really depends on a number of factors including pool usage, temperature, sunlight, etc. If you are worried about algae, you can do an Overnight Chlorine Loss Test (OCLT) to see how much you FC you lose between sundown and sunup. Anything more than a loss of 1 FC during the OCLT means your chlorine is battling something.

I would expect that as the water heats up and you start using the pool more, you will start losing more than the 1.2 daily loss you are seeing now. Consider taking your chlorine higher since 5 is the very bottom of your target and you want to make sure you are staying in your target range of 5-7 most of the day and stay far away from the minimum FC of 3. You may also benefit from upping your CYA to 50 or even 60, and adjusting your FC to the new target levels for those CYAs.


Silver Supporter
Mar 8, 2021
Chandler, AZ
Pool Size
Liquid Chlorine
My cya is at 40ppm and I'm losing 1.5 to 2ppm of FC per day. I think that's pretty good so far considering the pool is in full sun all day and it's been in the upper 90's.


Silver Supporter
In The Industry
Aug 15, 2017
Spring Valley, NY
I'd recommend getting the chlorine into the water in the morning to be ahead of the loss this way by days end you're still at the target level. Same theory goes for a heavy bather load, add some extra chlorine before the pool gets used so it'll never be in the danger zone after the get out.


Gold Supporter
Jun 28, 2017
Fresno, CA
Pool Size
FC demand is a moving target all year long. You can be sure it is somewhere between the summer peak demand and the winter low.
Toss in days with +30mph winds or a pool party with 10 kids and all bets are off. It's best not to assume too much and verify with the FAS-DPD test often.


LifeTime Supporter
TFP Guide
Feb 6, 2015
Chandler AZ
Pool Size
Liquid Chlorine
You may be better served to bring your FC to the high end of the recommended range. With CYA of 40, that would be FC of 7 according to the FC/CYA Chart. This will allow a bit of a buffer zone.

The overall goal is to NEVER let the FC go below the minimum FC for a given CYA. Being a little higher isn't a big deal as long as you don't go over the SLAM Process level (FC 16 for CYA 40).
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