Free vs Total Chlorine

[Myaimistrue]

My saltwater pool water is clear and there does not seem to be any problem with it. However, the drop test shows high ph and total chlorine. The digital test shows high ph and 0 free chlorine. When I add muratic acid the ph drops for a few hours, then returns. I have a 4m overflow, so I am wondering if that might be the cause? The internet says to shock it to free up some chlorine. Does that make sense to anyone?

 

 

 

[carlyai]

  On 1/28/2024 at 6:50 AM, Myaimistrue said:

My saltwater pool water is clear and there does not seem to be any problem with it. However, the drop test shows high ph and total chlorine. The digital test shows high ph and 0 free chlorine. When I add muratic acid the ph drops for a few hours, then returns. I have a 4m overflow, so I am wondering if that might be the cause? The internet says to shock it to free up some chlorine. Does that make sense to anyone?

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I don't think it will be a problem if you shock your pool.

When you digitally checked the pool, did you calibrate the test instrument first?

You need to get a test kit that you trust.

Takes a while but if you get all your pool parameters correct, then every weekend check again and just probably have to add some Soda Ash for PH.

 

[Myaimistrue]

  On 1/28/2024 at 7:39 AM, carlyai said:

I don't think it will be a problem if you shock your pool.

When you digitally checked the pool, did you calibrate the test instrument first?

You need to get a test kit that you trust.

Takes a while but if you get all your pool parameters correct, then every weekend check again and just probably have to add some Soda Ash for PH.

 

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No, I didn’t, I assumed it came calibrated. I did test it in a high concentration of chlorine and the free chlorine at least registered. In my water it only shows dashed lines or zeros. I will look into calibrating it, thanks for the suggestion.

[Bagwain]

Being a salt pool you will always have high pH. It is lowered by hydrocloric acid. By the look at the size of the pool in the picture, I would say, 1 cup + of acid twice a week should do the job. Try adjusting the amount to gain the best result. There are acid crystals available if you can source. Easier and safer to use.

 

If you don't keep the Ph down you run the risk of getting black spot which is a bane in the industry and hard to control! Get yourself some black algaecide and put a cupfull in every 3 - 6 months for insurance.

 

A salt chlorinator creates chlorine gas which in turn creates sodium hypochlorite (NaOCI) (Liquid chlorine "Bleach") This raises pH as apposed to 90% drychlor which has cynuric acid and lowers the pH.  You don't need any soda ash in your case.  

[Lacessit]

Once the pH gets above 9, there won't be any free chlorine around. To be effective, a pH of 7.5 is required.

 

Total chlorine is a measure of  the chlorine which has reacted with organics in the water, such as amines, to form chloramines. Total chlorine is far less effective than free chlorine as a bactericide.

 

The ideal free chlorine level is 0.1 - 0.5 ppm. ( mg/L ) More is not better, as it may cause eye and skin irritation.

[Myaimistrue]

  On 1/29/2024 at 3:20 AM, Bagwain said:

 

  On 1/29/2024 at 3:20 AM, Bagwain said:

Being a salt pool you will always have high pH. It is lowered by hydrocloric acid. By the look at the size of the pool in the picture, I would say, 1 cup + of acid twice a week should do the job. Try adjusting the amount to gain the best result. There are acid crystals available if you can source. Easier and safer to use.

 

If you don't keep the Ph down you run the risk of getting black spot which is a bane in the industry and hard to control! Get yourself some black algaecide and put a cupfull in every 3 - 6 months for insurance.

 

A salt chlorinator creates chlorine gas which in turn creates sodium hypochlorite (NaOCI) (Liquid chlorine "Bleach") This raises pH as apposed to 90% drychlor which has cynuric acid and lowers the pH.  You don't need any soda ash in your case.  

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Thanks, as I said, I have added muratic acid and the ph went down for a few hours but then returned to 7.9-8.1. I will look into the algaecide!

[Myaimistrue]

  On 1/29/2024 at 3:40 AM, Lacessit said:

Once the pH gets above 9, there won't be any free chlorine around. To be effective, a pH of 7.5 is required.

 

Total chlorine is a measure of  the chlorine which has reacted with organics in the water, such as amines, to form chloramines. Total chlorine is far less effective than free chlorine as a bactericide.

 

The ideal free chlorine level is 0.1 - 0.5 ppm. ( mg/L ) More is not better, as it may cause eye and skin irritation.

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Thanks, the pH has never gotten that high, usually high 7- low 8. How do I raise the free chlorine level without increasing the Total Chlorine level? 

[UWEB]

I have had the same problem with my new Pool. For the first 6 month I have used a Pool Service, but they never told me that there is a problem with high PH and low free Chlorine. Then I have started testing by myself and checked the complete System, here I found that my Chlorinater was running in Winter Mode. I changed to normal mode, since the problem with low Levels of free Chlorine was resolved.

Then I cleaned out the Balance Tank and Gutter, measured additional Salinity, Cyanuric Acid ,Alkalinity and Water Hardness and brought all step by step to the required Levels.

All has taken a while but now my PH is always between 7.3 and 7.8, here I add always 1 liter of Muriatic Acid to lower PH what is good for 8-10 days before I have to add Acid again.

[Lacessit]

  On 1/29/2024 at 7:41 AM, Myaimistrue said:

Thanks, the pH has never gotten that high, usually high 7- low 8. How do I raise the free chlorine level without increasing the Total Chlorine level? 

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I don't think you can. It depends on what organics are in the water supply which the free chlorine reacts with first to create Total Chlorine. Free Chlorine only comes into existence once the chlorine demand of the organics is satisfied.

 

I've seen Total Chlorine of 10 ppm, and 300 ppm. It all depends on the purity of the input water.

 

Chlorine effectiveness decreases quite rapidly above pH 8. It's the nascent oxygen of HOCl which oxidizes bacteria.

 

 

[Myaimistrue]

  On 1/29/2024 at 8:35 AM, Lacessit said:

I don't think you can. It depends on what organics are in the water supply which the free chlorine reacts with first to create Total Chlorine. Free Chlorine only comes into existence once the chlorine demand of the organics is satisfied.

 

I've seen Total Chlorine of 10 ppm, and 300 ppm. It all depends on the purity of the input water.

 

Chlorine effectiveness decreases quite rapidly above pH 8. It's the nascent oxygen of HOCl which oxidizes bacteria.

 

 

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I’m glad you brought up oxygen, that’s why I mentioned the large overflow. Could the water be getting over-oxygenated and lowering the efficiency of the chlorine?

[Myaimistrue]

  On 1/29/2024 at 8:04 AM, UWEB said:

I have had the same problem with my new Pool. For the first 6 month I have used a Pool Service, but they never told me that there is a problem with high PH and low free Chlorine. Then I have started testing by myself and checked the complete System, here I found that my Chlorinater was running in Winter Mode. I changed to normal mode, since the problem with low Levels of free Chlorine was resolved.

Then I cleaned out the Balance Tank and Gutter, measured additional Salinity, Cyanuric Acid ,Alkalinity and Water Hardness and brought all step by step to the required Levels.

All has taken a while but now my PH is always between 7.3 and 7.8, here I add always 1 liter of Muriatic Acid to lower PH what is good for 8-10 days before I have to add Acid again.

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Thanks! My chlorinator is in summer mode and at 100%. What are you using to measure your cyanuric acid? If test strips, which ones?

[UWEB]

  On 1/29/2024 at 10:53 AM, Myaimistrue said:

Thanks! My chlorinator is in summer mode and at 100%. What are you using to measure your cyanuric acid? If test strips, which ones?

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I'm using All in one Test Kit Pentair R151248 DPD78

[Lacessit]

  On 1/29/2024 at 10:45 AM, Myaimistrue said:

I’m glad you brought up oxygen, that’s why I mentioned the large overflow. Could the water be getting over-oxygenated and lowering the efficiency of the chlorine?

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Water has dissolved oxygen, IIRC about 8 mg/L in healthy water. That's not the same as the nascent oxygen generated by HOCl. The first is O2, the second is O.

 

Excessive aeration of a water reservoir will tend to drive off chlorine. It is a gas, after all.

 

Not knowing what your system looks like, I can't say what is happening with it.

[Myaimistrue]

  On 1/29/2024 at 12:11 PM, UWEB said:

I'm using All in one Test Kit Pentair R151248 DPD78

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Thanks!

[Myaimistrue]

  On 1/29/2024 at 12:43 PM, Lacessit said:

Water has dissolved oxygen, IIRC about 8 mg/L in healthy water. That's not the same as the nascent oxygen generated by HOCl. The first is O2, the second is O.

 

Excessive aeration of a water reservoir will tend to drive off chlorine. It is a gas, after all.

 

Not knowing what your system looks like, I can't say what is happening with it.

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Ok thanks, it does sound possible then. I think what I’ll do is dump some Sunblock in, cyanuric acid, and see what happens. I’ll shock it as a last resort.

[Bagwain]

  On 1/29/2024 at 1:13 PM, Myaimistrue said:

Ok thanks, it does sound possible then. I think what I’ll do is dump some Sunblock in, cyanuric acid, and see what happens. I’ll shock it as a last resort.

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You need to be mindfull of the cynuric acid levels. Too litlle or too much and it doesn't work. 

[Myaimistrue]

  On 1/30/2024 at 2:40 AM, Bagwain said:

You need to be mindfull of the cynuric acid levels. Too litlle or too much and it doesn't work. 

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Yes, thanks, I’m looking into that. Do you know the best way to test for it? My digital tester does not, so I“m assuming strips?

[Bagwain]

For a domestic pool, strips are fine. Just keep them in a cool place I.e. the fridge.

[1FinickyOne]

nice natural location...