Chlorine Consumption


Silver Supporter
Aug 7, 2009
Bloomington, IL
Do I have the following concept correct or am I missing something?

I understand that free chlorine consumption is by a percentage of free chlorine available. For example, I could lose ½ to 2/3 of my free chlorine per sunny day if the pool is exposed to the sun.

My CYA level is 40 using the turbidity test from Taylor. Therefore, my ideal FC range is 3 – 7 ppm. I test the chlorine level late in the day and add enough liquid chlorine to bring the FC level up to 7. So, theoretically, if I lose, for example, ½ of the FC per day, I would lose 3.5 ppm of FC. If I had brought the level up to 8 rather than 7 and lost ½ of the FC, I’d have lost 4 ppm of FC. From an economic standpoint, it seems I would be wiser to bring the level up to 7 rather than 8, provided I never dropped below 3 ppm.

Do I understand this correctly?



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

Yes, you explained everything just right.

Chlorine usage will vary somewhat over the cycle of the year because of changing water temperature, changing amounts of sunlight on the pool, more or fewer swimmers, etc. So the FC level you need to target to not go below the minimum 24 hours later will vary as well. What you described is the best you can do without trying it on your pool and seeing how things actually behave. Depending on what actually happens, you may need somewhat more or somewhat less chlorine.

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