How many PPM of Chlorine should I lose daily?

[chem geek]

Yes, this is quite reasonable. In addition to the thread KurtV referred you to, you can look at the following graph 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) 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. 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