Calcium Chloride and Free Chlorine

efm1972 · Jul 30, 2013

I added 4 lbs of Calcium Chloride at 1PM ET today to raise the calcium level in my pool. Test results before adding the Calcium Chloride were as follows:

FC = 4.0
CC = 0.0
pH = 7.6
CH = 200
Alk = 110
CYA = 40

Tonight, at 8:45PM ET, I started to test my water, but am not getting a reading for FC. Results as follows:

FC = 0.0
CC = 0.0
pH = 7.6
CH = 250
Alk = 110
CYA = 40

Can adding Calcium Chloride impact FC test result (or other test results)? It was a nice sunny day here today, but typically, I do not fall below 1.5 ppm for FC and I test FC daily. Water temp got to 78 today and the water is crystal clear.

Any insight as to why FC is zero would be much appreciated. I use 12.5% liquid chlorine was going to add enough to get to an FC of 7 ppm in the morning before I go to work and then retest again when I get home in the evening.

Thanks

Butterfly · Jul 30, 2013

Sometimes adding CH will cause some clouding, but not effect tests. But, possibly FC if the bag contents had some contaminants/unwelcomed organics.

With 40 CYA, keep FC between 3 and 7, and never below 3. Sounds like it has been dropping below the minimum.

I suggest you do an OCLT to rule out/in organics.

duraleigh · Jul 30, 2013

Any insight as to why FC is zero would be much appreciated.

What is your "normal" daily FC loss?

efm1972 · Jul 30, 2013

Thanks. I decided to shock pool tonight and added 2 gal liquid chlorine. Will retest FC in an hour and then again in the morning.

efm1972 · Jul 30, 2013

Normal FC loss is about 50%. If I start the day with FC = 4, it will usually be around 2 in the evening on a full sun day.

jblizzle · Jul 31, 2013

2ppm is too low for a CYA of 40ppm. Hopefully you pass the OCLT, but should maintain high FC levels going forward.

efm1972 · Aug 1, 2013

Thanks for the comments. Passed OCLT. I will now target to start day at FC of 6 or 7 ppm. That way (based on experience so far), I will end day around 3 ppm.

Also, given all the rain we had in the northeast (Philadelphia), I have had to drain over 6" of water off pool over the past several weeks. I was out of reagent for testing CYA, and hadn't checked it since June 29th. I just got some more reagent and my CYA is now 30.

Thanks again.