Chlorine Loss Due to Algae, SWG, low CYA or ???

[Liquid]

I recently had a warranty replacement on my SWG cell. The water is crystal clear, zero CC but lost about 1 FC in an OCLT test. Previously I had the SWG set to 30% but with the new unit it is currently set to 70% and barely keeping up. When checking my CYA it was low at 50 (target is 70) but hadn't raised it in the event I needed to SLAM the pool. Could the low CYA being the source of the FC loss, could it be algae, the SWG being faulty or something else? To note, I did an AA spot treatment (Vit-C pills in a sock rubbed on certain areas) to a couple places on the pool about a week ago. I'm in Florida and has been 90+ the last week. TF-100 results from this morning below:

PH - 7.6
FC - 4
CC - 0
TC - 4
CYA - 50
TA - 90
CH - 350
Salt - 3200

 

[mknauss]

We need pump run time and SWCG model to know how much FC you are adding to the pool each day.
A CYA of less than 70 for me and my FC loss nearly doubles in the summer. I would suggest you get your CYA to 70 ppm.

 

[Liquid]

Thanks for the reply. I have updated my signature with the specific model, which is a Jandy Aquapure PLC700.

I generally run the pump 7 hours/day. The pool gets very light use. I may jump in for a few mins on a given day. Should I increase the pump time in the Summer? I haven't been through a full year yet being in charge of pool maintenance so am not familiar with seasonal variations.

 

[mknauss]

At 70% and 7 hours, you are adding 3.6 ppm FC per day. Pretty normal for summer. Raise the CYA to 70 ppm and see how it works. With your small pool, UV, and warm water, the CYA will degrade 10-15% per month, so be sure to test monthly. And if you get overflow due to large rain storms, test more often.

I would suggest you run the pump and SWCG such that you are adding chlorine anytime the sun is shining on the pool surface, at a minimum.

 

[Liquid]

Thanks. Sock with stabilizer has been hung in the pool. When the pool was previously managed the SWG was set at 30% year round and when I first took over pool maintenance about two months ago (before the replacement SWG cell) the FC was running about 17/18. The pool maintenance company would write "5" for FC on the receipt every week...for the 13th months records I have. I'm learning, thanks for all the input.

 

[mknauss]

Likely the pool maintenance company added 'shock' each week. Standard practice.

 

[Liquid]

Thanks for the heads up