2 For 1: Chlorine & Borate Questions

Jul 21, 2019
NYC Area
Fire and foremost - the TFP forum has been so helpful to me since buying my home last year with my first pool that I am considering changing my username to something that more accurately reflects my transformation from "clueless" to "almost have a basic idea of what I am doing".

With that said - I have two questions:

1. At home, I have stopped using trichlor and have been using CYA. I did not empty my pool out so my CYA is still at 100 ppm from. Last year with TriChlor in a slow feeder I almost never had a dip in chlorine. This year, exclusively using bleach, I have been dropping chlorine a lot (or what seems like a lot). We did install a heat pump and we do experience full sun, so maybe that plays a roll. With that said, at 81 degrees in 64 degree air temp, over night (taking measurements after sun down and before sun hit the pool in the AM) my chlorine dropped from 11.5 ppm to 10.5 ppm. Is that drop "normal" for 14,500 gallons in that water temp/air temp or should I suspect that I have algae growing but undetectable? The water does look crystal clear and feel great, but I have had moments where through the day my chlorine was dropping from 11ppm to any where between 3 and 6ppm during full sun and use so I have grown nervous.

2. At work, I am generally responsible for a 660,000 gallon pool. I say generally because I am not the pool operator or technician, but they do answer to me. Before I found TFP I would never make suggestions to these experience folks, but after TFP and personally using borates to improve water quality, I am left wondering if I should direct us to use borates in our pool to improve balance, chlorine demand, and water "feel" for bathers. Can anyone think of a down side to borates in large commercial pools? If you would use it, how would go about getting 2,500 lbs + of borates into the pool for 50 ppm borates - or should I aim for a lower number to start?

Thank you all!


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
You failed the overnight loss test. Remember, two things consume chlorine: Sunlight and organics. You removed sunlight as a potential cause. What's left?

Now comes the rub. To eradicate whatever it is means the SLAM Process and that's going to be real difficult with 100 CYA. You say the water looks great, so concentrate immediately on the places where algae could hide. Don't waste days brushing and gallons of bleach failing the OCLT again and again before you dig in.

Borates: not a clue. Don't use 'em.