Lower chlorine level with Sodium Sulfite

[swimmy22]

In preparation of closing, I accidentally added twice as much chlorine as I needed to get FC up to SLAM level for my CYA. (I have a feeling that I had the calculator set at 6% chlorine instead of 12.5%). I put the cover on after adding the chlorine so I wouldn’t have to vacuum the pool out again before closing so the chlorine is not likely to go down any before it is closed in a few days. Even if I took the cover off, the FC isn’t likely to go down by half before closing since the closing is in 3 days and the water is cold. FC is 40 and I need it to go down to 20 by Monday.

I called my pool guy and he recommended that I lower the FC with a chlorine reducer that is sold at pool stores before closing. The one that they have at my pool store contains Sodium Sulfite but I am only seeing information on here about Sodium Thiosulfate. Is this the same thing? I haven’t found any pool stores that sell Sodium Thiosulfate and I don’t have time to get Sodium Thiosulfate delivered before closing so I hope Sodium sulfite will suffice. Before I go out and purchase something to lower the chlorine level, I need to know what the effects of adding Sodium sulfite would be to my water chemistry. Could it alter the PH, TA, CYA, or phosphates after it is added or cause any issues with my water? I also need to know if it can be added in front of a deep end return instead of spreading it evenly around the pool like the instructions on the bottle recommend. The cover is already on the pool so it would be easier to dissolve it in a bucket of water and pour it into the pool in front of a deep end return. I also need to know if I need to run the pump for 24 hours after adding it. The guy at the pool store says to run the pump for at least 30 minutes after adding it but the water is cold so I was wondering if I should run the pump longer than that.

 

[JamesW]

1 qt of hydrogen peroxide will lower it by about 1 ppm.

About $1 per quart.

 

[Bperry]

In preparation of closing, I accidentally added twice as much chlorine as I needed to get FC up to SLAM level for my CYA. (I have a feeling that I had the calculator set at 6% chlorine instead of 12.5%). I put the cover on after adding the chlorine so I wouldn’t have to vacuum the pool out again before closing so the chlorine is not likely to go down any before it is closed in a few days. Even if I took the cover off, the FC isn’t likely to go down by half before closing since the closing is in 3 days and the water is cold. FC is 40 and I need it to go down to 20 by Monday.

I called my pool guy and he recommended that I lower the FC with a chlorine reducer that is sold at pool stores before closing. The one that they have at my pool store contains Sodium Sulfite but I am only seeing information on here about Sodium Thiosulfate. Is this the same thing? I haven’t found any pool stores that sell Sodium Thiosulfate and I don’t have time to get Sodium Thiosulfate delivered before closing so I hope Sodium sulfite will suffice. Before I go out and purchase something to lower the chlorine level, I need to know what the effects of adding Sodium sulfite would be to my water chemistry. Could it alter the PH, TA, CYA, or phosphates after it is added or cause any issues with my water? I also need to know if it can be added in front of a deep end return instead of spreading it evenly around the pool like the instructions on the bottle recommend. The cover is already on the pool so it would be easier to dissolve it in a bucket of water and pour it into the pool in front of a deep end return. I also need to know if I need to run the pump for 24 hours after adding it. The guy at the pool store says to run the pump for at least 30 minutes after adding it but the water is cold so I was wondering if I should run the pump longer than that.

I’d leave it alone, or add some CYA to buffer it a bit more if it makes you more comfortable.

 

[swimmy22]

1 qt of hydrogen peroxide will lower it by about 1 ppm.

About $1 per quart.

Is it better to use hydrogen peroxide to lower the FC than Sodium Sulfite? If so, what are the effects of adding hydrogen peroxide compared to the effects of adding Sodium Sulfite and what Is the best way to add it? It looks like I can get a quart of Sodium Sulfite chlorine reducer for about $18 which will lower the FC to my desired level which is 20 ppm. If a $1 bottle of Hydrogen peroxide will lower the FC by only 1 ppm, it looks like it would cost me $20 to lower the FC by 20. Since the cost is about the same, I’d like to add whichever one would have the least harmful effects to my water chemistry and can be added in front of a deep end return.

 

[swimmy22]

I’d leave it alone, or add some CYA to buffer it a bit more if it makes you more comfortable.

I’m curious to know why you say to leave it alone because I thought TFP recommending closing at SLAM level and it is 20 ppms over SLAM level. If I wanted to add CYA to buffer it, wouldn’t I have to increase the CYA really high to buffer 40 ppms of chlorine? I’ve got a chlorine pool so I don’t want the CYA too high so I can use tablets on vacation.

 

[JamesW]

There is virtually no effect on the chemistry.

The pH might drop a tiny bit, but that is all.

2H₂O₂ + OCl^-+ HOCl --> 2O₂ + 2H₂O + H⁺ + 2Cl^-

 

[JamesW]

 

[swimmy22]

There is virtually no effect on the chemistry.

The pH might drop a tiny bit, but that is all.

2H₂O₂ + OCl^-+ HOCl --> 2O₂ + 2H₂O + H⁺ + 2Cl^-

Why are you recommending hydrogen peroxide over adding sodium sulfite? I couldn’t find any information on here or anywhere else for that matter regarding the effects of adding either one and how to add it to my pool. I’m closing in 2 days so I don’t want to add anything that could mess up my water chemistry or cause other problems before closing. I wanted to add polyquat at closing but i know that the FC is way too high to use that now so I thought I’d get FC down to SLAM level instead.

 

[JamesW]

Why are you recommending hydrogen peroxide over adding sodium sulfite?

There is virtually no effect on the chemistry.

The only effect is lowering the FC and maybe a tiny bit of pH drop.

In my opinion, it is the easiest and cleanest way to drop the FC.

 

[JamesW]

Sulfite becomes sulfate, which I would avoid.

 

[Bperry]

I’m curious to know why you say to leave it alone because I thought TFP recommending closing at SLAM level and it is 20 ppms over SLAM level.

Cause it’ll probably go down on its own over the next few weeks. It’s still gonna be pretty warm for the next month.

 

[swimmy22]

Sulfite becomes sulfate, which I would avoid.

Please forgive my ignorance but what do sulfates do to your water? How do I add hydrogen peroxide if I decided to use that instead? Can it be poured in front of a deep end return? How long does the pump need to run after adding it? It makes me nervous if you say that it might drop the ph because it would be hard to increase the PH with the cover on since baking soda is applied by broadcasting it around the perimeter. Ph tends to go down over the winter in my pool because I have a mesh cover that lets rain into the pool so I wouldnt want to close with low PH.

 

[JamesW]

Please forgive my ignorance but what do sulfates do to your water?

It's not a big deal to have some sulfate, but a lot can lead to calcium sulfate scaling and other issues.

How do I add hydrogen peroxide if I decided to use that instead? Can it be poured in front of a deep end return?

Yes, just add it in front of the return.

How long does the pump need to run after adding it?

An hour or so is plenty.

 

[swimmy22]

Cause it’ll probably go down on its own over the next few weeks. It’s still gonna be pretty warm for the next month.

I can’t imagine that the FC will go down enough to matter since the water is cold and it is covered by a mesh cover Rainfall might lower it a bit but not by much unless we get an excessive amount of rain. Could a FC of 40 bleach the fiberglass or damage the fittings if I decided not to lower it? I read something on another post about high chlorine bleaching liners and fiberglass and damaging fittings so closing with such a high chlorine level concerns me.

 

[JamesW]

Using sulfite will have the same effect on pH as using the hydrogen peroxide.

2Na₂SO₃+ OCl^-+ HOCl --> 2SO₄^2- + H⁺ + 2Cl^- + 4Na⁺

 

[JamesW]

What is your current pH and TA?

 

[Bperry]

I can’t imagine that the FC will go down enough to matter since the water is cold and it is covered by a mesh cover Rainfall might lower it a bit but not by much unless we get an excessive amount of rain. Could a FC of 40 bleach the fiberglass or damage the fittings if I decided not to lower it? I read something on another post about high chlorine bleaching liners and fiberglass and damaging fittings so closing with such a high chlorine level concerns me.

Someone else would have to comment on what double SLAM level chlorine actually does but SLAM level FC is safe to swim in so I have a hard time believing that fiberglass would be negatively impacted by elevated chlorine for a short period of time assuming the pool equipment is off and drained. My only potential concern would be a heater. I’m still losing about 1ppm per day and I’m just a bit south of KY. I’d guess your FC would be back at SLAM level or lower in a week or two at most.

Maybe check the FC again and see if you can estimate a daily loss and decide if you want to take action to lower it.

 

[swimmy22]

Someone else would have to comment on what double SLAM level chlorine actually does but SLAM level FC is safe to swim in so I have a hard time believing that fiberglass would be negatively impacted by elevated chlorine for a short period of time assuming the pool equipment is off and drained. My only potential concern would be a heater. I’m still losing about 1ppm per day and I’m just a bit south of KY. I’d guess your FC would be back at SLAM level or lower in a week or two at most.

Maybe check the FC again and see if you can estimate a daily loss and decide if you want to take action to lower it.

Please excuse my ignorance but why would our water lose FC if the pool is covered by a mesh cover and the water is below 60 degrees? We were only losing 1 ppm of chlorine before we put the cover on so it seems like it won‘t lose much chlorine now that the cover is on and is keeping sun and organics like leaves out of the pool. I’d like to know what the risks would be with closing with a double SLAM level because I don’t want to add hydrogen peroxide or a chlorine neutralizer if they could alter the ph or cause other problems. I know that rainfall will lower the chlorine some but it would take a lot of rain to get the FC to drop by 20.

 

[Bperry]

Please excuse my ignorance but why would our water lose FC if the pool is covered by a mesh cover and the water is below 60 degrees? We were only losing 1 ppm of chlorine before we put the cover on so it seems like it won‘t lose much chlorine now that the cover is on and is keeping sun and organics like leaves out of the pool. I’d like to know what the risks would be with closing with a double SLAM level because I don’t want to add hydrogen peroxide or a chlorine neutralizer if they could alter the ph or cause other problems. I know that rainfall will lower the chlorine some but it would take a lot of rain to get the FC to drop by 20.

Chlorine degrades in the bottle at the store in the dark. Light and heat just make it go even faster. It’s unstable so that’s just what it does over time.

 

[swimmy22]

3It's not a big deal to have some sulfate, but a lot can lead to calcium sulfate scaling and other issues.

Yes, just add it in front of the return.

An hour or so is plenty.

What is the dosage for lowering the chlorine with 3% hydrogen peroxide that you find at a drug store? I don’t see any information on the pool math calculator regarding it so I need to know how much to add to lower the chlorine level by 1 ppms so I can calculate the dosage after testing the chlorine level. Are you sure that it is safe to add in front of a return and it won’t harm the fiberglass if it isn’t brushed in or poured around the perimeter of the pool? If it ends up dropping the PH too much, is there a way to increase the PH before closing without taking the cover off? I cant get an accurate PH reading because the FC is so high but it was 7.6 before I added the chlorine. It makes me a bit nervous to add something to my pool that it not sold in pool stores so I want to make sure it won‘t cause any problems. I postponed the closing to see if the chlorine level would go down but it still too high. It’s going to drop below freezing next week so I’m closing on Friday and would like to lower the chlorine level back down to SLAM level before everything is winterized. I don’t want to risk closing above SLAM level since high chlorine can supposedly bleach out gelcoat like it can bleach a liner.