High Chlorine

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norsehorse

Well-known member
Aug 16, 2022
62
Middle Tennessee
Pool Size
20000
Surface
Fiberglass
Chlorine
Salt Water Generator
Hey Folks -

I made the mistake of leaving my SWG at 1% over the last few weeks, and my FC count is over 50PPM. The pool is covered. I purchased some sodium thiosulfate which should get here in a couple days. Should I avoid diluting the pool through backwashing and refilling? Is PPM at this level safe to work near or are there additional precautions I should be taking to avoid inhaling anything unsavory? Or does that not matter due to it being an outdoor pool that gets uncovered for at least a few minutes before I work on it? The fiberglass is fine and other than my dolphin looking a little lighter in color, there doesn't seem to be any issues I can see from the high chlorine count. CYA count is also low, so hoping it will burn off and normalize over the next week.

Thanks!
 
Thanks mknauss. Nothing I should be worried about safety wise with an FC count that high? My wife was freaking out I was going to inhale some chlorinated gas, lol.

Sounds like I can just stick to plan of backwash, refill, and wait for sodium thiosulfate to arrive.

**edited to add that the SWCG has been turned off for 2 days, will plan to keep it off until it's balanced.
 
I would leave the pool uncovered until FC is down again so that any gases can gas off. Or is your cover a safety cover that needs to stay on?
 
Thanks mknauss! Appreciate it. Mgtfp, it's a safety cover, so it needs to stay on when we can't visibly see the pool. I'll be keeping it open the next few days, but it needs to close up at night.
 
Don't mess with safety. Drowning is a much bigger health hazzard than a few chloramine gases. Just open the cover a couple of times a day.
 
Just out of curiosity: What is your water temperature over winter? I guess the safety cover helps to keep it up a bit.

Generally a lucky position to be in, being able to run the SWG through winter. You just need to work out how many hours per day on which setting to maintain a reasonable chlorine level.

In Australia we usually keep our pools open all year, and our SWGs are designed to run through winter without cold-water-shutdown (they may not reach max output, but that's hardly needed).

My pool is fully shaded over the winter months, but no cover. Water temperature down to about 8°C (46°F). I have worked out that during this period where the pool is in full shade with practically no UV and cold water, my pool uses about 0.25ppm of FC per day (at FC 10ppm). That means I have to run my SWG for about 4-5 hours per day on its lowest setting (12.5%) or about 2-2.5 hours on the next higher setting (25%). That keeps my FC around 10ppm all winter. Short run times may be a bit trickier with the US SWGs that adjust output via duty cycle rather than current control.

After some more diligent testing over the first winter to understand how my pool behaves, I now test about once a fortnight.

Makes the pool really trouble free over winter.
 
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It's about 43 degrees F right now. I think the initial issue was at overwintering, I left the SWG at about 5% for a week before cutting it down after turning off the heater. With the heater cranking in the fall, it burns plenty of FC every day. I don't use CYA really because even in the summer, the pool is closed unless we are in it. So, it's really just me balancing FC and TC most of the year. That said, I will likely change that up this year.

I could choose to heat it right now, but being an electric heater, it doesn't function well below 50 degrees F, so I just keep it shut off until late Feb. or Early March. I haven't gone out to learn how to program my salt cell to only run for a few hours per day, but that's probably a smart idea in order to keep everything balanced.
 

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norsehorse said:
It's about 43 degrees F right now. I think the initial issue was at overwintering, I left the SWG at about 5% for a week before cutting it down after turning off the heater. With the heater cranking in the fall, it burns plenty of FC every day. I don't use CYA really because even in the summer, the pool is closed unless we are in it. So, it's really just me balancing FC and TC most of the year. That said, I will likely change that up this year.

I could choose to heat it right now, but being an electric heater, it doesn't function well below 50 degrees F, so I just keep it shut off until late Feb. or Early March. I haven't gone out to learn how to program my salt cell to only run for a few hours per day, but that's probably a smart idea in order to keep everything balanced.
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How is your SWG making chlorine when it’s so cold still? How sure are you about the 50ppm? You counted 100 drops of reagent?
 
Yep, counted over 100 drops of regent before it started to dissapate. I just ordered a two new bottles. I really wanted to know what I was dealing with. SWG likely was making chlorine when the temps would stay above a certain level. In Tennessee we can have 60 degrees for 3 days and down under 10 three days later. They always say if you don't like the weather here, wait a few hours.
 
OK, understood. Probably best to then just manually turn the SWG off over winter and switch to liquid chlorine so you know how much and when chlorine is added.

I'd recommend to add some CYA, even if you don't need it for UV protection with your cover. CYA will take the harshness out of chlorine.

Without any CYA you have a very small operating window for your FC levels. Target FC would be like 0.1ppm, SLAM FC would be 0.64ppm. 50ppm without CYA is quite a lot.

With let's say 40ppm CYA you have a target FC around 5ppm and a SLAM-FC of 16ppm. 16ppm with 40ppm CYA has the same concentration of "active" chlorine (which is HOCl) and therefore the same "harshness" as FC 0.64ppm without CYA. You have a much wider operating window and an accidental 50ppm event is far less consequential.

With CYA, the bulk of the chlorine is bound to CYA where it doesn't really do anything, but unfortunately still shows up as FC in the test. This means you have a small amount of "active" chlorine and a huge chlorine reservoir that replenishes the active chlorine as it gets used up.
 
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norsehorse said:
Yep, counted over 100 drops of regent before it started to dissapate. I just ordered a two new bottles. I really wanted to know what I was dealing with. SWG likely was making chlorine when the temps would stay above a certain level. In Tennessee we can have 60 degrees for 3 days and down under 10 three days later. They always say if you don't like the weather here, wait a few hours.
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Must be warmer over there, it’s been below 50 for a few weeks prior to this.
 
Bperry, prior to the snowstorm we had a few days above 50. Then pretty much right afterwards we shot up to 55-60 degrees and rainy. It's definitely been a warmer winter compared to last season.
 
norsehorse said:
Bperry, prior to the snowstorm we had a few days above 50. Then pretty much right afterwards we shot up to 55-60 degrees and rainy. It's definitely been a warmer winter compared to last season.
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That’s so weird. It was unseasonably cold over here for two straight weeks.
 
With low CYA, you could get a floater and use tabs to chlorinate the rest of the winter. I have one going on mine right now to maintain chlorine and add a bit of CYA to be ready for swim season in a couple of months.
 
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