Solar Cover Creating Chemical Imbalance

[bxcrwlly]

For the last two years, in October, when my solar cover has been on the pool for a couple of weeks, I've noticed my chlorine level drops to zero. With a SWG, this is not good, so I start adding liquid chlorine. I read some old posts 2008 and prior regarding negative impacts to pool chemicals with covers. The posts seem to focus on potential algae development both on or below the cover causing excessive amounts of chlorine depletion. I also read a posts citing a reduction in the ability of the sun and the chemicals to correctly interact causing a problem.

In my case, I don't ever have visible algae and normally my chlorine level is maintained at 5ppm. I could certainly supplement the SWG with liquid to ensure proper level maintenance while the cover is deployed. I live in Florida and normally only use the cover in late fall and early spring for 3-5 weeks each season to extend pool use. My pool store suggested trying the "liquid cover." After reading numerous articles, on this site and others, reviews seem to be mixed as to the effectiveness and chemical contribution to the pool, so I'm leery regarding its use.

Looking for advice about how to handle. Should I remove the cover "x" number of times per week as a matter of course to let the pool "breathe" or simply enhance chlorine dosing with the liquid?

 

[Donldson]

Have you noticed an increase of CC when your FC drops? That would be my guess to the issue since sunlight normally burns off CC but without direct sunlight your FC must take care of it. Without seeing the numbers myself I can't be sure. Have you run an OCLT to verify it isn't qn organic problem?

Assuming no organic problems, all 3 options you gave are viable and have their pros and cons. The best, IMO, would be to take your cover at least partly off during a sunny day a couple times a week. Adding extra chlorine will get the job done as well. I am not a fan of liquid solar covers, but it could provide you a benefit. It reduces evaporation somewhat so does decrease some heat loss and shouldn't interfere with the sunlight. Might work, might not, those things are very hit-and-miss.

From my HTC One via Tapatalk

 

[chem geek]

It sounds like your cover may not be clean if you are finding chlorine consumption to be high. Usually with a cover you get lower chlorine consumption because of less loss due to sunlight but you will see chlorine consumption remain because of slow chlorine oxidation of the cover itself. If the cover has debris or is old and decaying, then you could have significant chlorine consumption from that.

You might consider targeting a higher FC level when using the cover just in case the problem is indeed algae growth on the underside of the cover. You could also point your returns slightly up to make sure there's good circulation hitting the cover.

 

[JoyfulNoise]

I would also note that you have a roughly 12k gallon pool with a Pentair IC-20 SWG. While the IC-20 is supposed to be able to handle pools up to 20k gallons, experience has taught us that most SWG's are undersized for pools. I have a 16k gallon pool and I use an IC-40. When it's time to replace the cell, I will likely get an IC-60.

My thinking here is that, if your cover is not clean or if the FC has to do the extra work of oxidizing organics due to less UV from the sun (as the others have mentioned), then you SWG may not be able to keep up with the higher demand. How often are you running your pumps and what output % is your IC20 set to?

 

[bxcrwlly]

Thanks all for your feedback. Here's some answers to your comments/questions.

Donldson - No increase in CC. No organics involved.

chem geek - Pool is enclosed with screen cage, so only dust, pollen, etc. get through. No visible algae growth anywhere on cover. No cover deterioration. Will ramp up my FC during covered periods.

JoyfulNoise - Pump running 8 hrs. daily around 1800rpms unless solar heating, then 2800rpms. IC20 set based on year over year stats using temp averages, etc. Generally without cover between 25-30% for this time of year. Have now boosted to 50% with cover and supplementing with liquid if necessary. Salt level around 4000ppm. I too will replace my IC20 with an IC40 when required. It's now 3 years old. I hear the lifespan is around 5 years.