Can gelcoat on a fiberglass pool be harmed from high chlorine levels?

Can you cover the pool while you are away? Take it to SLAM level, turn off equipment then cover the pool.

an1vrsy said:

Can you cover the pool while you are away? Take it to SLAM level, turn off equipment then cover the pool.

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Just pointing out that unless the cover is one that can be stretched and suspended above the water, the leaves lying on the cover will still be lying in the pool water, and will still be affecting the chlorine loss. I don't know off-hand if using a cover to keep leaves from getting to the bottom will reduce the organic load on the chlorine, but if it does it won't be by much. Now keeping the sun off the water will help with chlorine loss, so used in that way, a cover might help.

We have a reliable calculator about how much you can raise your FC (based on your CYA level). We refer to the max recommended FC as "SLAM level." We maintain it is safe to raise your FC to SLAM level. And by "safe" we mean for humans and for your pool. Raising FC above that can damage your pool and equipment. How much above, for how long and how much damage is not something we could accurately predict. If you did it once a year, probably not a big deal. If you did it every weekend, then, yah, you could bleach your gel coat.

Also, the FC above SLAM level burns off pretty quickly, because it is beyond the "protection" the CYA is providing, so goosing your FC above SLAM level is not really the best way to accomplish your goal, for a couple reasons. Raising it above the maximum normal recommended level, but at or below SLAM level should be fine.

So try SLAM level, and maybe a cover, and see how it goes. If you get back on Monday and you're still above the normal target FC level, then you're golden. You could even experiment by reducing the amount of FC you're using on Friday, so that you don't go higher than you have to. If you can't maintain FC in this way, you risk an algae outbreak and will need some other strategy.

gwtw said:

I have a couple of more questions. How far in advance should we get the pool up to shock level before turning off the pump and leaving for the weekend? Should we get it to shock level an hour before we leave or earlier in the day?

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The standard answer is circulate for 30 minutes. An hour is plenty.

gwtw said:

If it doesn't end up being windy and we don't get many leaves in the pool, will we likely lose the same amount of chlorine with the pump off than we normally do with the pump on?

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Pretty much. Once the chlorine is mixed in, it goes to work. More pumping (or no pumping) doesn't really affect that process, except as follows.

Even though the crud gets sucked up and sent into the skimmer basket, or the pump basket, or the filter for the small stuff, it's still in your water, and the chlorine is still trying to "eat it."

There may be other factors in play, but basically your FC loss is determined by sunlight and organic load. Unless you remove the organic load, wherever it is, it's still going to be causing FC loss.

Now, theoretically, if you turn off your pump, the crud in your filter will use up the available chlorine in the filter itself, but will no longer be using up your FC out in the pool. So if your filter was filthy, and you weren't running the pump, in theory your pool will lose less chlorine than if you were running the pump. In real world, it'd be hard to say if this would make any significant difference.

Might need @mknauss to "check my math" on that hypothesis.

Bottomline, a residential pool's chlorine-based sanitation process is designed to work in tandem with its circulation system. Turning off the circulation will likely cause more harm than not when it comes to keeping your pool safe and sanitary, there's really no way around that. You'll likely get away with turning the pump off for a few days now and then. If this is an every-weekend thing, than we might need to explore a more reliable method. How often do you do this?

Keep in mind, in a perfect storm, like if you left on a Friday afternoon and it was mid-summer and crazy hot, and a flock of geese land in your pool and attract a family of raccoons, and they all go to town, even SLAM level FC can vanish pretty quickly, certainly over a weekend. You're basically playing the odds that nothing goes wrong while nobody is watching the pool. Those aren't bad odds, but it's still somewhat of a gamble.

This is where remote pool automation, an SWG, a pool webcam and a trustworthy neighbor or family/friend come in handy.

Hey, I'm not kidding. Check out this raiding party. The brown one is a raccoon in disguise. They're fiendishly clever.

gwtw said:

Looks like the safest thing to do in this situation is to just get it to shock level, turn off the pump and pray that the chlorine lasts two days.

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You could also let your CYA drift down a bit in advance and then fill one or two floaters with tabs to help supplement.

MITBeta said:

You could also let your CYA drift down a bit in advance and then fill one or two floaters with tabs to help supplement.

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Based on my experience with permanently staining my pool finish with liquid CYA, I would not let tabs float in my pool without circulation. I don't know if a floater full of tabs can leach enough acid and chlorine such that it would drift straight down and collect in one spot on the bottom, but I wouldn't want to experiment with that in my pool. Maybe others will know.

Even if this was safe to do, I'm not sure how that's a sustainable solution if the OP is leaving his pool for many weekends, or most weekends.

gwtw said:

Thanks for all of the advice everyone. I went away for the weekend, got it to shock level for my CYA beforehand, and turned off the pump. I came home 2 days later and my FC was 1 ppm above the minimum FC level for my CYA and water looked crystal clear. I lost slightly more chlorine than I would with the pump on but I contribute this to the fact that the pump was off, leaves blew into the pool, and we found a dead bird floating in the pool.

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Yah, there are wild cards. Even with the best laid plans, leaving a pool unattended has its risks. You just experienced two of 'em. Fortunately it was only a bird. Glad it worked for you, though. And now you have a good data point for next time.

Do you have anyone that can attend the pool while you're away? Not regularly, I mean someone that could respond to an emergency situation? I had mentioned before: a wifi cam can go a long way toward peace of mind. Point one at the pool and check on it a few times while away. You won't see a bird in the skimmer, but you can spot a floating whatever out in the pool, or maybe some other strange occurrence that just can't wait for your return. You might not be able to call on someone to leaf rake, or fish out a dead raccoon, but if the problem is bad enough, maybe you'd want to know so that you could return early, rather than come back to a much bigger problem a few days later.

I went overboard (as I tend to do) and have a PTZ (pan, tilt, zoom) cam on my pool. I see everything, even right down into the water! "Hi Rebel, bottom looks nice and clean, good work last night! Go ahead and take the rest of the day off."