High Chlorine Loss - Is my SWCG not working properly?

[smkz]

We've been having a huge heat wave in central FL over the past few weeks, and as expected I've seen chlorine consumption in my pool increase. I have been inching up the SWG (RJ 30+) power level but seem to continue slowly losing FC, and I've finally reached 100% power but even this still seems like it's not sufficient. Very different from last year when it was able to maintain FC at 50% power even during peak summer.

My water is clear, nothing has been added (other than LC) and there's no visible algae, contamination etc. No one has swam in it for a week either. The seemingly obvious explanation is that I need to SLAM because there's something brewing, and I plan to do that this weekend if I can't figure it out before then, but... I have a weird suspicion that my SWG may not be making enough chlorine. I did a somewhat unscientific experiment testing FC from a spot in the middle of the pool and comparing it with water collected straight from the closest return jet with the SWG on. The difference was only 0.5 FC, which seems like too small of a delta to me? At that rate one full turnover would add .5 FC to the pool... assuming it's running at full power the whole time. This does not seem like sufficient generation to keep up with a sunny day to me, unless I'm missing something?

Overnight my FC is holding steady... With the SWG running at 100%! (Pump on very low speed, just enough to trigger flow switch). With an estimated 1 water turnover overnight, and a .5 FC loss due to the extremely warm water (ending the day at 92F), this sort of tracks with my suspicions. I'll try a true OCLT tonight with the SWG off.

The SWG appears to be functioning properly: While running it produces bubbles like normal, voltage and amps are within spec, no errors on the controller and the cell is clean.

Water stats per TF-Pro:
FC 8
CC 0
PH 7.6
TA 80
CYA 80
CH 300

Salt is 3600, both my handheld tester and the RJ+ system agree on that.

I'm not sure how to explain this one. If the FC out of the jets was significantly higher but the overall pool FC was dropping then that's easy, SLAM time. But this is making me question if the SWG is working properly. Should I just SLAM anyway, should I clean the cell even though it looks good, something else?

If anyone has experienced a similar situation before I'd love to hear about it. Thanks!

 

[Newdude]

I'll try a true OCLT tonight with the SWG off.

GREAT.

If you fail, then there's your answer.

Report back with results.

 

[smkz]

I went out and pulled the cell for closer inspection. It does look like there was a very fine film of calcium deposits on some of the fins, impossible to see without the cell removed and me staring straight down into it. I went ahead and cleaned the cell (first time I've ever done it, had system for 1.5 years and keep my CSI slight negative).

One thing I failed to mention before that I'd recently noticed but didn't think much of: the bubbles coming out of my returns were slightly bigger than the usual carbonation fizz that I'm used to. After returning the cleaned cell to plumbing and turning it back on, the tiny fizz bubbles are back. I suspect I've solved it but will do a OCLT overnight still.

 

[smkz]

OCLT passed with <=0.5 FC loss overnight. I also redid my testing with water closest to the SWG return and it's showing 4 PPM higher than the rest of the pool now, as opposed to 0.5 before.

Not sure how the extremely tiny bit of calcium buildup on the cell was making that much of a difference, but apparently it was!