Chemical reaction confusing

[donaldm823]

Yesterday (7/18), I added 6lbs of Leslie CaCl (casting it over the deep end) to raise my CH hardness back above 200ppm. I did this two days AFTER of shocking my pool (the chlorine level (FC) had decreased to 5.71 (at 1315 on a sunny day). Today(5/19) (at 1015) I sampled and my chlorine (FC) was 1.28ppm with TC at 1.46ppm. This drastic drop in 22hr was much more than expected (expecting 2.5ppm)as chlorine levels were going down about 40% each day due to the sun and also CC went up to 0.25 from 0.0ppm. 2 weeks ago I added 9lbs of CaCl from the same Leslie bucket and chlorine went down 3ppm (I thought it was an algae bloom starting). Is there any known chemical reaction when adding CaCl for raising hardness? In both cases, my hardness went up as, but chlorine took a drastic drop and appeared as a large chlorine demand. Or could it be a contaminated chemical?

Here is yesterday and today's sample results. Note that I added 7.5 gal of 6% Chlorox on the night of 7/16 (15ppm increase over the 1.7ppm FC present)
I have a 30000 gal in ground pool (1 yr old) with a DE filter and 2hp pump. I also am running TA intentionally low since pH creeps up above 7.7 with TA at 80.

7/18 (@1315)sample
FC 5.71
TC 5.78
TA 64
pH 7.5
CH 198
CYA 38

7/19 (@1015) sample
FC 1.23
TC 1.46
TA 63
pH 7.5
CH 207
CYA 45

[chem geek]

There shouldn't be any reaction between calcium chloride and the chlorine in the pool. So I don't have an explanation for what you saw.

Richard

[CarlD]

You are assuming that you aren't fighting something else. Your chlorine dropped a lot, fast. That tells me your best move is to shock the pool again.

[donaldm823]

You are assuming that you aren't fighting something else. Your chlorine dropped a lot, fast. That tells me your best move is to shock the pool again.

I reshocked again at 1615 yesterday with a 180oz jug of chlorox (2.8ppm). Based on chemistry this morning my chlorine was constant over night (FC=4.78 and TC = 4.92). It appears no chlorine demand overnight as my add should have taken the pool to approx 4.9 and the CC also went down, so the drastic decrease from yesterday is still unexplained.