Use of Hyrdogen Peroxide in Pool Water with high FC

[KCNM]

Moved from here.
It looks lighter than your first picture to me.

The best thing to do is let the sun's UV rays burn it off. That's good for a few ppm a day, max. This will be mediated by your CYA levels, which stabilizes the chlorine against UV rays. That's why woodyp is asking about your CYA levels. Since we don't have an accurate reading of your chlorine other than "high", we can't even attempt to predict how long this might take.

There are chemicals that can neutralize the chlorine directly, but they have drawbacks. For instance, I would not recommend using hydrogen peroxide to neutralize without knowing your PH. That is because hydrogen peroxide converts the chlorine directly into hydrochloric acid.

Free Chlorine - Further Reading

www.troublefreepool.com

 

[JoyfulNoise]

There are chemicals that can neutralize the chlorine directly, but they have drawbacks. For instance, I would not recommend using hydrogen peroxide to neutralize without knowing your PH. That is because hydrogen peroxide converts the chlorine directly into hydrochloric acid.

This statement is misleading at best. Peroxide does not create hydrochloric acid when it neutralizes chlorine but it can lower pH slightly. The reactions are as follows -

Peroxide reacting with hypochlorite anion -

ClO− + H2O2 ---> Cl− + H2O + O2​

hypochlorite + peroxide ---> chloride ion + water + oxygen gas​

and peroxide reacting with hypochlorous acid -

HClO + H2O2 ---> H+ + Cl− + H2O + O2​

Hypochlorous acid + peroxide ----> hydronium ion + chloride ion + water + oxygen gas​

Since pool water with chlorine and stabilizer is a mixture of hypochlorous acid and hypochlorite anion, the amount of pH lowering hydronium ions (H+) created depends on the starting pH and the amount of peroxide used. While the pH will decrease, it will not decrease rapidly and it certainly is not creating anything dangerous.

There is no need to panic here. Very likely what has happened in this pool is that pucks were overused and now the chlorine is very high and the pH and TA are very low because pucks are acidic. The fix is to leave the chlorine alone as the sun and time will burn it off. You should check the TA immediately and, if it is very low you should bring it up to at least 60-80 ppm. The addition of sodium bicarbonate will restore the pH slowly especially if the pool is well brushed.

 

[KCNM]

This statement is misleading at best. Peroxide does not create hydrochloric acid when it neutralizes chlorine but it can lower pH slightly. The reactions are as follows -

and peroxide reacting with hypochlorous acid -

HClO + H2O2 ---> H+ + Cl− + H2O + O2​

Hypochlorous acid + peroxide ----> hydronium ion + chloride ion + water + oxygen gas​

No disrespect, and I'm no chemist... But I'm not sure how you can write H+ and Cl- as results of that reaction as independent ions with a straight face. Those two ions will be attracted to each other, and when combined would be... Hydrochloric acid.

References I can find for this reaction shows them combined:

HClO + H2O2 = H2O + O2 + HCl |

Hypochlorous acid react with hydrogen peroxide to produce water, oxygen and hydrogen chloride. Chemical reaction. Balancing chemical equations.

chemiday.com

Second formula on the right:

Hypochlorous Acid - an overview | ScienceDirect Topics

www.sciencedirect.com

 

[JamesW]

I'm not sure how you can write H+ and Cl- as results of that reaction as independent ions with a straight face. Those two ions will be attracted to each other, and when combined would be... Hydrochloric acid.

The ions do not need to be combined to be hydrochloric acid.

Even in a bottle of hydrochloric acid, the ions are not combined to any significant degree.

The only relevant ion is the hydrogen ion, which will lower the pH some, but not significantly, which was already acknowledged.

So, yes, you get the equivalent of adding a tiny amount of acid, which people do all the time.

When acid is added, it does not remain as acid circulating in the water waiting to come into contact with something.

It just lower the pH and TA some depending on the amounts added and the starting TA.

Also, the reactants are already well dispersed and you never even get any concentrated amount of acid at all.

 

[KCNM]

I can understand that maybe it's not an *important* amount of acid. That's a fine thing to say. I only took offense to post I responded to making it seem like the reaction was not generating HCl at all. And since we have no idea the balance of this pool other than "high chlorine", I thought it worth mentioning.

And of course, HCl is such a strong acid *because* it so readily separates and recombines.

 

[JamesW]

and peroxide reacting with hypochlorous acid -

HClO + H2O2 ---> H+ + Cl− + H2O + O2

Hypochlorous acid + peroxide ----> hydronium ion + chloride ion + water + oxygen gas

I only took offense to post I responded to making it seem like the reaction was not generating HCl at all.

The post clearly indicated the chemicals produced.

The reaction does not really produce "hydrochloric acid" because hydrochloric acid is concentrated.

Once the ions are dispersed in water, they are not considered to be hydrochloric acid.

However, I don't consider it wrong to say that hydrochloric acid is produced because it is producing the same thing and it's mostly semantics.

 

[JoyfulNoise]

No disrespect, and I'm no chemist...

By your own admission, you are not a chemist...

Free hydrogen ions (H+) do not exist in dilute aqueous solutions, they are always in the form of hydronium

H⁺ + H₂O <---> H₃0⁺

It is simply a shorthand convention to write the acidic proton as an individual hydrogen ion so as to not confuse. But the reality is that ions do not just float around in solution. As well, chloride ions do not "stick" to other ions when in dilute solution, they are solvated in a shell of water molecules since water has a dipole moment due to its bent structure. Because of these realities, it doesn't really matter in solution that the counter ion is chloride. As @JamesW alluded to, hydrochloric acid is mostly a concentrated chemical where the hydrogen ion and chloride ion DO exist in their bare ionic states and form a tightly bound ionic compound. I tend to disagree with James' assertions that is is semantics ... its not. Ions and atoms behave very differently depending on how concentrated they are in a solution.

Therefore the reality of the reaction between peroxide and chlorine is that there will be some production of hydrogen ions that will lower pH ... hydrochloric acid has nothing to do with it.

 

[KCNM]

By your own admission, you are not a chemist...

Free hydrogen ions (H+) do not exist in dilute aqueous solutions, they are always in the form of hydronium

H⁺ + H₂O <---> H₃0⁺

It is simply a shorthand convention to write the acidic proton as an individual hydrogen ion so as to not confuse. But the reality is that ions do not just float around in solution. As well, chloride ions do not "stick" to other ions when in dilute solution, they are solvated in a shell of water molecules since water has a dipole moment due to its bent structure. Because of these realities, it doesn't really matter in solution that the counter ion is chloride. As @JamesW alluded to, hydrochloric acid is mostly a concentrated chemical where the hydrogen ion and chloride ion DO exist in their bare ionic states and form a tightly bound ionic compound. I tend to disagree with James' assertions that is is semantics ... its not. Ions and atoms behave very differently depending on how concentrated they are in a solution.

Therefore the reality of the reaction between peroxide and chlorine is that there will be some production of hydrogen ions that will lower pH ... hydrochloric acid has nothing to do with it.

I started typing a response, and I'm deciding instead to just stop. Because this pendantry is not helpful for anyone. It lowers the PH of the pool. That was my only point. No further discussion necessary on the mechanism by which it does that, and that mechanism's potential similarity with what someone might call hydrochloric acid.

So, to restate my original claim in what is hopefully acceptable terms:

I wouldn't advise an action that could potentially lower the PH of the pool when I don't know the PH or TA of the pool.

 

[JamesW]

I tend to disagree with James' assertions that is is semantics ... its not. Ions and atoms behave very differently depending on how concentrated they are in a solution.

Therefore the reality of the reaction between peroxide and chlorine is that there will be some production of hydrogen ions that will lower pH ... hydrochloric acid has nothing to do with it.

If you have 32% hydrochloric acid and dilute it by half, you then have 16% hydrochloric acid.

If you continue to dilute it by half, you get 8% and then 4%, 2%, 1% and so on.

At what point is it no longer hydrochloric acid and it is just water?

The net result of adding hydrogen peroxide is the same as adding hydrochloric acid.

You are increasing the amount of hydrogen ions and chloride ions.

 

[JamesW]

I wouldn't advise an action that could potentially lower the PH of the pool when I don't know the PH or TA of the pool.

I can agree that the pH is probably already too low and you would not want to lower it more, so your concern is valid.

However, the chlorine is very high and it can be especially corrosive to metals like copper when the pH is also low, so the high chlorine itself creates a hazard, especially if the pH is really low.

Also, you are not going to get a valid pH test while the chlorine is that high, so I would go ahead and drop the chlorine to below 10 ppm and then get a pH, TA and CYA reading and begin to address the numbers as needed.

Adding the hydrogen peroxide will not drop the pH by a lot and you are going to bring it up right away with baking soda, so the pH will only go a little bit lower for maybe 30 minutes.

 

[JamesW]

Waiting for the sunlight to reduce the chlorine reduces the pH just as much as using hydrogen peroxide.

2HOCl + UV --> 2H⁺ + 2Cl^- + O₂

So, there is no benefit to waiting for the sun to reduce the chlorine vs. using hydrogen peroxide.