SWG not producing

[dschmitt]

My FC keeps dropping and I cannot figure out why my SWG doesn’t appear to be producing properly. We have had several gatherings at the pool so I have been doing band-aid work to nurse it along but now I need to figure this out.

It began about a month ago. FC dropped to 0.5. Was able to get it back into shape by SLAM. Salt was low so I added a bag to bring it back into spec. Also checked the SWG and noticed deposits so I cleaned it. Also increased my SWG output to 60%. Figured that took care of it and it held steady for 2-3 weeks.

About a week ago it slipped to 2.5. CYA had dropped to 55, so I added the required amount. With all the sun we’ve had lately, that seemed to be the problem.

But today it’s down to 1.5, with pH also a bit low at 7.5.

I need to SLAM again - it’s cloudy and smells a little brackish. But before I do that I want to make sure I’ve figured out why the SWG isn’t producing.

The only thing I can think of is whether there is enough salt. I ran out of salt test solution, but have some strips and they are reading around 3800, and the SWG is reporting 3500. So I think I’m ok there.

One other thing: we have been keeping the pool heater at 84 this season. I wouldn’t think that would matter but that’s something different that we did this season.

Below is tonight’s test results. Thoughts, suggestions on what to do next?
------------------------------------------
Build Type: Plaster
Volume: 30000 gallons
------------------------------------------
Latest Test Result Summary:
FC: 1.5 (2 hours ago)
CC: 0.5 (2 hours ago)
pH: 7.5 (2 hours ago)
TA: 80 (2 hours ago)
CH: 350 (2 hours ago)
CYA: 80 (2 hours ago)
SALT: 3500 (5 days ago)
TEMPERATURE: 85° (2 hours ago)
CSI: -0.29 (2 hours ago)
==========================================

 

[Jimrahbe]

d,

While your SWCG could be bad, the number one reason for a cell not producing enough chlorine is algae.

A cell can never make more chlorine than algae can consume..

You should really only have to SLAM once... It sounds to me like you believe that your SLAM is complete, but I suspect that it has not been successful... I recommend that you review the SLAM requirements and see if there is anything you missed.

Thanks,

Jim R.

 

[generessler]

Yeah your SWG maxes out at 5.6 ppm per day. You're running at 60% (24 hours a day?), so 3.3 ppm if the cell is working perfectly. For Texas that seems marginal even with no algae. At CYA 80, your min is 4, when you've seen 2.5 recently. If you didn't have algae before (which as @Jimrahbe said does not seem very likely), you almost certainly do now. SLAM time, I think. Good luck with it.

 

[jmastron]

If you're looking for definitive numbers, you could do a set of 3 experiments after you complete a successful SLAM:

1) OCLT (Overnight Chlorine Loss) -- this will be part of the SLAM completion anyway, to confirm that you have little to no loss without sun.

2) OCGT (Overnight Chlorine Gain) -- run the SWCG at 100% overnight, and measure FC before and after. With some math, that will tell you how much it's generating per day, which can either point to a problem with the SWCG or confirm none.

3) (optional) On a typical sunny day, bring the FC to ~9-10ppm (to provide a margin), turn the SWCG *off* for that day, then measure FC at sunrise and sunset. That will show your inherent daily FC usage. Matching that against #2 can tell you how long and what percentage to run the SWCG at. Note that this will vary considerably by month/season as the sun angle and temperature changes.

SWCG or not, you should be testing often enough to catch the FC level getting too low, and address that as priority. If that means adding liquid chlorine, do so. And if the data says you have to run the SWCG at 100% to keep up in peak months, don't hesitate to do so. It won't break the unit (I leave mine at 100% always and use a timer to control the runtime) -- yes it uses up more cell life, but it does so generating the chlorine that you'd otherwise need to go buy to supplement (or SLAM) anyway.

 

[dschmitt]

Thanks all for your advice. This forum is awesome.

Started my SLAM today. Because I knew it was going to be a couple of days before I get to it, I put my SWG at 100% just to see if it would produce. FC rose all the way to 8, so looks like it’s definitely able to produce, and as you suggested, I’ve got algae consuming faster than it could produce. (Not that I doubted you!)

 

[dschmitt]

Quick update — SLAM complete and pool is back in shape. Will be testing SWG at 100% overnight to make sure it’s ok, but I think I just wasn’t paying enough attention and didn’t SLAM properly before.

Again, thanks to all for your help.