How many PPM of Chlorine should I lose daily?

[keithw]

I have switched to the BBB method recently. Pool looks great, thanks for the great info! I have a 6000 gal fiberglass, sand filter, partial sun. Pool temp is 84ish. Here are my Taylor K-2006 readings.

CYA 95-100
ALK 210
PH 7.5
Salt 2470
FC 5.6
CC. Real low barely registers. Maybe .2
Calcium 0

I have been testing same time each day for past few days. I appear to lose 2.7 PPM Chlorine daily. I add 3ish cups each day to get back to 8ish PPM.

Seem reasonable? I realize that my CYA is out of whack but plan on leaving it be for this season and correcting with a partial drain over winter.

[KurtV]

Chlorine depletion thread. (http://www.poolforum.com/pf2/showthread.php?t=5117)

[chem geek]

Yes, this is quite reasonable. In addition to the thread KurtV referred you to, you can look at the following graph (http://richardfalk.home.comcast.net/pool/HalfLife.png) to see that the half-life of chlorine at an FC of 8 ppm with a CYA of 100 is almost 8 hours if there were full noontime sunlight the entire time (which there isn't). Half of 8 is 4 ppm and you are losing about 2.7 ppm so that seems reasonable.

Though the high CYA level helps to prevent chlorine loss, this same high CYA level also requires you to maintain rather high FC levels (from Ben's Best Guess CYA chart (http://www.poolforum.com/pf2/showthread.php?t=365)) and the net effect is a higher absolute chlorine loss per day. The only way to solve this problem is to lower your CYA level as you can see from the following graph (http://richardfalk.home.comcast.net/pool/ChlorineLoss.png). Ben's chart is around 0.04 ppm HOCl for the 8 ppm at 100 ppm CYA so your loss rate is around 0.8 ppm/hour at peak. If you were to get your CYA down to 30 ppm, then you could maintain a minimum chlorine level of 3 ppm which lowers your chlorine loss rate to about 0.3 ppm/hour at peak which is less than half your current rate. (The graph makes it look like you should go down to 0 ppm CYA for a minimum chlorine loss, but you simply cannot maintain a 0.05 ppm HOCl or total FC of 0.1 ppm throughout your pool at all times so must use some CYA as a "buffer" to hold extra chlorine -- usually you don't go below 2-3 ppm FC).

So at some point you will want to get your CYA lowered, at least down to 50 (if not 30) and unfortunately you have to partially drain and refill your pool with fresh water in order to do that (and, of course, do not use Tri-Chlor tablets).

Richard