Been running this SWG for a couple of seasons and generally like it very much. For whatever reason, I happened to notice a discrepancy this year & thought I'd ask the sages here...

The Pool Calculator targets FC at 4 for a SWG. The Pool Pilot manual suggests 1-3. I'm currently running mine at power level 1 and 75%. With those settings I'm only able to keep FC at 2.4, even with the solar cover on.

Complete readings are:
FC 2.4
CC 0.2
PH 7.6
TA 120 (working on that - added acid today & going to aerate)
CH 280

So the question is whether I should be bumping up my SWG power level to get to a higher FC...

Thanks in advance for any guidance!

What is your CYA level? This kind of issue is extremely sensitive to the CYA level, which should be 70 to 80.

You will have a noticeably lower chance of getting algae at our recommended levels.

If you do need to turn up the percentage any further, you should increase the power level to 2.

Another possibility, less likely for the moment, is that you have a low level algae problem.

Thanks for the quick response!

Sorry, I did forget the CYA - it's been around 60-65 (always a bit hard to read that test). I assume, though, that the CYA isn't as important when the solar cover is on. (?) Hence my mentioning that the FC level didn't go up even with the cover on. Maybe I'm wrong about that, though.

I did have an unusual algae bloom this spring - not sure why. This is the first season that's ever happened to me. Anyway, I was able to clear it up in a couple of days and things have appeared to be okay since. (Looks good, walls not slippery, etc.).

I don't mind bumping up the CYA and the power setting... It's just that I've run at this power setting in the past and had higher FC. But maybe it's getting burned up with some low algae as you suggest.

Some solar covers are UV opaque, others let UV through. CYA isn't nearly as important if the cover is UV opaque. If your cover was UV opaque and you don't have a low level algae problem, your FC level would be out of control high, so either your cover is UV transparent or you have a low level algae problem. You should do an overnight FC loss test to see if there is any algae/organic problem.

Huh. I didn't realize that some covers don't block UV. Mine is a 12 mil clear one - just bought this year. I don't know about it's UV rating - I'll have to see if I can find out. Will do the overnight test tonight.

Last night the FC went from 2.8 to 2.4. No CC this morning. Based on Pool School, it looks like there's little to no activity going on. I guess I need to bump the power level & see what happens next...

What did you use to clear up the algae? Sodium Bromide based products are detrimental to salt chlorination systems.
When you run a TEST POOL PILOT, what does the unit show as the salt level, and the the Cell Amps and Volts?

Hi Sean,

I just used regular bleach, brushing & my Aquabot. Ran the pump continuously until things cleared & backwashed twice.
Test shows 3200 salt, 6.4 amps, 21 volts. That's with the power now set at 2.

Thanks!

Amps and volts are withing the normal operating range. Sounds like a chlorine demand condition that superchlorinating can help out. Have you ever tested for Phosphates? High levels of phosphates, especially with Algae is present, will cause a demand for chlorine.

No, I've never tested for phosphates... Might have to pick up a test kit for that - thanks for the suggestion. Meanwhile, yesterday afternoon's readings were:

FC 5.4
CC 0
pH 7.1 (I'm aerating to bring it back up after adding acid for the TA)
TA 100
CH 240
CYA 70+ (added CYA on Friday, so it probably isn't fully accurate yet)

We also got over 2" of rain on Friday night. So setting the SWG at the second power level definitely helped with the FC situation. When I made the power change I also reduced the percentage setting from 75% to 45%. I think I'll back it off a bit more yet.

Phosphates don't have anything to do with it unless your FC level is marginal to begin with.

Puzzling update:

Our weather got cool & rainy the past week or so, so the solar cover's been on all week. Looked underneath yesterday and I've got the beginnings of green algae on the walls/bottom again!

Readings as of yesterday afternoon:

FC 3.4
CC .2
pH 7.1
TA 90
CH 260
CYA 70

I put the SWG on a boost cycle as an immediate step. Should I consider shocking it for a number of hours using bleach to keep the level up?

WTH's going on?? I've never had algae like this.

FC of 3.4 with CYA of 70 might be too low. I think I just read a thread where chem geek suggests at least FC 4.0 with CYA at SWG range (60-80). This jives with the "best guess" FC vs CYA chart.

Is the SWG cranked up to max and only maintaining 3.4? Or is there more room to increase it?

You probably do need to shock, with a high CYA level its gonna require a decent amount of bleach. I dont think Id rely on the SWG for this.....maybe turn it off completely while running with straight bleach for a few days.

You you should shock the pool, and make a point of brushing everywhere. Also, leave the cover off while at shock level.

Keeping the cover on all the time makes it more difficult to keep things working normally. I can't tell for sure if that is part of your issue or not, but it seems likely.

Thanks for the advice... Wow - I just did the calculation to see how much bleach I need to get it to shock level The cashier's gonna give me a funny look...

Try a local pool store (I know, I know!!) to see if they have the 5 gallon jugs of 12.5%. I know our local Namco has them, 17.00 for the chlorine + 6.00 refundable deposit when you bring back the empty. Decent price, but more importantly an easy way to get a lot of liquid chlorine.

Good idea! Now that you mention it, I remember doing that once before. My local pool store has 2.5 gal for around $11.

Still bugs me, though, that my CC is nil and my overnight FC loss is also very low. Sigh.

Anybody know how long it takes the shock level to dissipate? I have swimmers coming on Sunday...

You can use a chlorine neutralizer (Jacks Magic aftershock) to bring the chlorine level back down, after you treat your pool for at least 24 hrs. Be VERY conservative with how much you add though, as it can create a chlorine demand that can drop out your chlorine level.

Shocking has begun!

BTW, I don't know if this is related, but we've had numerous honeybees hanging around the pool this spring. They hang out on the solar cover & if the cover's off they end up drowning in the pool. Never happened before. I can't really figure out why. Maybe they smell a low level algae that doesn't really register on CC & overnight FC??