SWCG Production

[rdavis75]

Opening was painless this year. Water is balancing and behaving as I would expect based on my results last year. Current results:
FC = 3
CC = < 0.5
PH 7.6
TA 110
CYA 40
CH 425

My question is this. Last year I ran my SWG at around 10% with the pump running full time at 50 GPM. I routinely had FC readings around 6 or 7. I could easily take FC up to near slam levels at full production and leaving the cover closed during daylight. This year I’ve got the SWG running at 100% with pump at 50 GPM 24 hrs and I’m not breaking 3 to 3.5 FC. Admittedly my CYA is down a bit and I’ve got 4 lbs going in the pool this evening via sock/return.

The pool was finished in July of last year when temps were already hot. I assume, since the SWG won’t produce if it’s too cold, that there is an efficiency effect on chlorine production based on water temp, which today was up to 77 or so. Temps last year temps were typically 84 to 88. Can the lower temps be having that large of an effect on chlorine production in the SWG or is there something else going on I should be concerned with?

 

[needsajet]

Nice to meet you via TFP

Most likely is nascent algae, but you can easily rule it in or out, by doing this test: Overnight Chlorine Loss Test (SWCG must be off during the test)

Free-floating algae is invisible to the naked eye, but can be easily detected with that test.

 

[needsajet]

I meant to mention we'd ordinarily hold off on the CYA until after the OCLT in your situation. It's OK either way, but if a SLAM is needed, it's a bit easier at lower CYA.

 

[rdavis75]

Understood on the CYA/SLAM. However, I was quite a bit low for my pool and my addition likely will only make about a 10ppm difference in my CYA level which will be rather negligible on liquid chlorine requirements to SLAM, at least from a $ standpoint.

With no visible signs of algae, and frankly never have had a sign of any, I would anticipate a very quick SLAM. The water is perfectly clear and CC’s are well under 0.5 (barely any hint of pink after the 2nd reagent addition) so with doing nothing I’m passing 2 of the 3 criteria. And with my low CYA, a FC of 3.5 is probably adequate with the cooler temps.

I’m going to raise to SLAM levels in the morning (based on my CYA levels per my addition tonight) and maintain all day and then run OCLT tomorrow night.

My original question remains. How much of an impact does water temp have on the efficiency of the SWG? Quantitatively, what does a 10 degree water temp difference make on chlorine output with all other things being equal?

 

[jblizzle]

There is not much of an impact on production. It mostly either produces or does not.

The lower CYA means you will have larger losses to the sun, so that is one factor. Is it reading proper salt levels relative to your testing?

 

[needsajet]

I haven't noticed a temperature effect on SWCG output myself. I know theoretically there's an effect but negligible in practice. People run them through winter here with water in the mid-50s F (low teens C)

You can do the OCLT without raising FC first, but if you do, be sure to measure starting FC after enough time for mixing of the added chlorine. In other words, don't rely of calculated FC level for OCLT start.