SWG Chlorine Generation Rate

[GregoryRG]

I'm wondering if the output of my SWG is correct. I'm looking for a sanity check on my math:

My water chemistry today was (evening measurement time):

pH 7.5
FC 3.0
CC 0.5 (or less)
TA 80
CH 75
Borates 40 to 50
CYA 70 to 80 (between 70 and 80 on the black dot/graduated cylinder test)
Salt - 3000 ppm

The FC was 5.5 at 8:15 AM before the sun hit the pool. It was basically sunny with a max temp of 82F. The pool saw sun from 10:00 to about 5:30 to 6:00.

I ran the system 10 hours last night from 9:00 PM to 7:00 AM. It is an all or none system (no ability to regulate FC generation as a percentage).

The specs for the SWG state a maximum sanitizer output of 11 grams/hour. So the amount of chlorine (assuming 100% efficiency) would be 110 grams. Therefore, for my current chemistry, using the pool math calculator (set to chlorine gas - mass is mass), it appears I should have had a gross FC rise (assuming zero consumption overnight) of approximately 5.8 overnight. YET, my FC was 5.5 this AM and 2.5 the night before for an estimated generation of 3.0 FC (assuming no overnight losses). The CC is very low, so I can't believe what is basically an OCLT would say I'm losing 2.8 FC overnight! So, obviously, my SWG isn't putting out chlorine efficiently. In fact, the numbers basically say the output is only (3/5.8 x 11) or 5.7 g of Cl per hour run-time. The unit is less than a month old, and appears to be clean. The manual's statement on the SWG is:

"The titanium electrode and E.C.O. electrodes have a self cleaning function incorporated into the electronic control’s programming. In most cases this self cleaning action will keep the electrodes working at optimum efficiency. If the pool water is hard (high mineral content) the electrodes may require periodic manual cleaning. To maintain maximum performance, we recommend that you open and visually inspect the titanium and E.C.O. electrodes once per month."

I don't appear to have hard water, unless they are talking about other minerals beside calcium.

The specs for the pump/SWG system cover up to a 14K gallon pool and our is only 5K gallons. In fact, the manual specifies an 8 hour SWG run time for a 14k gallon pool (at 84 to 97F ambient air temp). So, I cannot see how this thing could keep up with a larger pool (it's maximum SWG run time is 12 hours).

Any thoughts? Am I missing something? Could my SWG be defective?

The manufacturer's "ideal" salt level is 3000 ppm (I measured 3200pm about 1.5 weeks ago, it is 3000ppm today), and I know the TFP guidance is to run the salt about 400 ppm higher than spec'd, but could this be a contributing factor to what appears to be poor FC generation? The rest of the chemistry numbers seem to be good to very good.

Thanks,

Bob

PS - I forgot to confirm the FC drop during the day today was 2.5.

 

[chem geek]

11 grams/hour in 5000 gallons is 0.58 ppm FC per hour. So yes, 10 hours overnight should have raised the FC by 5.8 minus overnight loss which should normally be small (usually less than 0.5 ppm at regular non-SLAM FC/CYA levels). You could do an OCLT with the SWG off to confirm, but yes it does seem like the SWG might not be outputting what it is supposed to.

 

[DaninFLA]

chemgeek has you covered, but wanted to add that your FC of 3 is too low for your CYA. you need to bump it up a bit. since you don't have ability to change percentage, only option is to change run time. I would manually raise your FC level with bleach and then allow your SWCG to maintain it.

I have CYA of 70-80 and I keep my FC range from 6 to 8. I test in the evening after the SWCG is done and confirm my FC is 8. lowest it drops to during the day is about 6.

as far as salt levels go, if you salt level is making your SWCG happy, no need to change it. if it gives error code for being too low, you need to add salt. most SWCG can operate fine with salt levels well above its ideal range.

 

[GregoryRG]

Thanks. I'll be testing, adding bleach this PM to bump up the "baseline" FC and then running the SWG. Overnight last night, it seems to have put out about 4.5 ppm FC (FC was 7.5 with basically zero CC this AM). I seem be losing 2.0 to 2.5 ppm FC during the day with 8 to 10 hours of direct sunshine this time of year (temps have ranged from low 80's to low 90's since I got the water balanced).

So, I'm going to double check my testing methodology to ensure I'm consistent in how I add the reagent drops, etc. with my drop test. Might be some testing error on my part. But, 4.5 ppm is still pretty short of the 5.8 ppm theoretical output (assuming little to no overnight consumption). I'm doing an OCLT test Saturday night. If all this checks out, I'll be calling Intex on Monday about my SWG system...

 

[DaninFLA]

the theoretical output you will probably never hit, you are doing pretty good. water temperature affects the cells performance as well. you are 1.3ppm off the theoretical output, that's a pretty small amount to detect with testing.

a number of issues can affect your FC testing. First off the FC test is probably +/- 0.5ppm at that range for accuracy, plus if you have 9.3ml or 10.7ml of water instead of 10ml (very easy to do by the way), that would be a change of around 0.4ppm in test results. plus your pool even without algae could be using up 0.5-1.0ppm of FC during the night. 4.5 of the 5.8 is pretty good I think.