Why Is Copper Sulfate Incompatible With Hydrogen Peroxide?

[radante]

Chemically-speaking, why is Hydrogen Peroxide counterindicated as a shock treatment when copper sulfate is used as an algaecide?

[radante]

Perhaps it isn't?

I'm thinking that Copper Sulfate as the main algaecide, combined with a 30% Hydrogen Peroxide weekly shock (or daily), would suffice as an algaecide, oxidizer and biocide.

[chem geek]

Both copper and iron metal ions are incompatible with hydrogen peroxide because of Fenton-like reactions. For copper, this is described in this paper. Basically, the metal ions catalyze hydrogen peroxide destruction to oxygen gas and water. This paper goes into detail for the Fenton reaction when iron ions are present.

Hydrogen peroxide is not a great biocide for pools and spas. You need the concentration to be at a rather high level of 100 ppm to have fast enough kill times for some bacteria (still not enough for others), but at that level it can also be irritating. See this paper showing hydrogen peroxide not to be effective in swimming pools and this paper explaining why some bacteria are not killed by hydrogen peroxide and this paper that showed some killing when combining hydrogen peroxide and silver ions, but still too slow for some pathogens unless the hydrogen peroxide concentration were 30,000 ppm which is way too high. See also this thread and this thread both describing damage to hot tub components when using hydrogen peroxide.

[radante]

Chem Geek,

Isn't the Fenton's Reagent reaction a good thing? It is true that in the presence of a transition metal such as copper, hydrogen peroxide will react much more vigorously and aggressively than without the metal (acting as a catalyst) ... and this dramatically increases the oxidative strength of hydrogen peroxide. Won't this increase in oxidation power create numerous hydroxyl radicals (OH•) that will destroy the chemical bonds of all organic compounds in the pool very quickly?

Also, can't Hydrogen Peroxide and Sodium Hypochlorite work synergistically on pathogens? (as described here): Synergistic antifungal activity of sodium hypochlorite, hydrogen peroxide, and cupric sulfate

Finally, doesn't copper contribute to chlorine decay?

[chem geek]

If the intent is to have more oxidation, then yes having metal ions plus hydrogen peroxide will result in hydroxyl radicals, at least when iron is used. If you read the paper I linked to, when copper is used there aren't many hydroxyl radicals produced, at least at a pH of 8.0 (there may be more produced at lower pH). Instead with copper it's superoxide anion (O₂•^-) which is not as powerful an oxidizer as hydroxyl radical (OH•). So if you are going to want a Fenton reaction, you'd use iron instead of copper. Of course, if you want hydroxyl radicals, there are other ways of getting those including use of ozone that decays in part to hydroxyl radicals or use of boron-doped diamond electrodes with electrolysis or the use of titanium dioxide in the water.

By the way, when the UV in sunlight breaks down chlorine, it produces hydroxyl radicals (see this post). So with chlorine you get the best of both worlds -- you get very fast disinfection from hypochlorous acid (HOCl) and you get some hydroxyl radicals in outdoor pools. This is one reason why it's fairly easy to have very low active chlorine levels in outdoor residential pools and keep them very clean and clear with minimal combined chlorine and little buildup of organics. It's not enough to handle higher bather loads as with commercial/public pools so there supplemental oxidation systems (such as ozone) can be used to reduce the production of chlorinated disinfection by-products.

As for hydrogen peroxide and chlorine, these also react with each other and in fact hydrogen peroxide is an easy way to reduce chlorine levels. The link you gave was not a combination of these but rather SEQUENTIAL application of first sodium hypochlorite and then hydrogen peroxide with copper sulfate. It took lower levels of each when used in this sequential combination, mostly because of the one-two punch for killing via different mechanisms that prevent the organism from inhibiting just one of these chemicals. The pathogen in question was not a human one but a fungus on citrus.

Copper by itself does not contribute to chlorine decay in dilute solutions as found in pools. Metal ions in general do catalyze decay of concentrated hypochlorite solutions (i.e. chlorinating liquid or bleach) where they specifically catalyze the decomposition pathway of hypochlorite to oxygen gas. The usual decomposition pathway without such metal ion catalysts is to chloride and chlorate.

It sounds like you are trying to use something other than chlorine for disinfection (and oxidation). Why are you trying to do that? Do you realize that with Cyanuric Acid in the water and with the Free Chlorine set to prevent algae growth regardless of algae nutrient (phosphate and nitrate) level (so an FC/CYA ratio of 7.5%) that the active chlorine level is the same as with an FC of only 0.06 ppm with no CYA? Why would you want to try and eliminate such a low level of chlorine when it is incredibly effective against human pathogens as well as in preventing algae growth?

[radante]

Indeed, I have (had) a mental block about chlorine...hence my turn to Hydrogen Peroxide. It's widely used in Europe as a pool disinfectant. The main issue with HP is its lack of lasting, residual power. It acts quickly, but like you said, you need a much greater volume and concentration for it to be fully effective. Still, with copper sulfate keeping my algae in check, the amount of Sodium Hypochlorite needed to keep my FC at 0.5 PPM or lower, should be extremely low. With a low bather load, I'm wondering if I would need to add a little liquid chlorine everyday at dusk or just a greater amount weekly. But I'm starting to think that simply Copper Sulfate Pentahydrate with Sodium Hypchlorite and the occasional acid to keep PH in check will suffice. I just ordered the K-2006 kit, so I'll be in a better position to know what's going on once it arrives.

[chem geek]

If your goal is just to minimize the chlorine level, and again you need to stop thinking about FC as that level since it is not (it's the FC/CYA ratio that is relevant), then you can use other means to control algae and then have a lower FC/CYA ratio. While copper will control algae, it can also stain plaster surfaces and turn blond hair greenish so I wouldn't use it if you have a plaster pool or if people with blond hair use the pool. You could instead use a phosphate remover that would accomplish the same thing for algae control.

So if you want a lower active chlorine level with these supplemental products preventing algae growth, then target around 2-3% for your FC/CYA ratio. You should set your CYA level high enough so that you don't use up too much chlorine during the day. So that means 1 to 1.5 ppm FC with 50 ppm CYA, for example. It makes absolutely no sense at all to try and keep the FC at 0.5 ppm -- again, FC is meaningless and only tells you the RESERVE of chlorine, NOT the active amount of chlorine that reacts with swimsuits, skin, and hair. If you go too far, say to 0.5 ppm FC with 100 ppm CYA, then you will not only have so little reserve that it could get to zero too easily, but the active chlorine level will be low enough for some pathogens to grow and possibly biofilms to form. You don't want to push it too far.

And you are wrong about (only) Europe using hydrogen peroxide. DIN 19643 which is the German standard used in many countries in Europe for commercial/public pools uses chlorine, NOT hydrogen peroxide. In Europe, just as in the U.S., you can do whatever you want in your own private pool just like you can leave a chicken out on the counter for hours and then cut vegetables in its juices and the government isn't going to do anything about it. In a commercial kitchen, however, there are rules for preventing people from getting sick just as there are for commercial/public pools. So this idea that hydrogen peroxide is used (only) in Europe is simply baloney -- it is used in the U.S. along with other "alternatives" in private pools such as metal ion systems (by themselves such as Pristine Blue), enzymes (e.g. ClearChoice), surfactant biofilm removal systems (e.g. Aquafinesse), etc. The only thing about the U.S. (and Canada) is that these alternatives cannot claim to be disinfectants. Some of these companies, particularly those promoting metal ion systems, got into trouble with the EPA and now have to qualify their bactericidal claims with "*Nonpublic Health Bacteria".

By the way, the DIN 19643 standard uses 0.3 to 0.6 ppm FC but with no CYA and with ozone it's 0.2 to 0.5 ppm FC. The 2%-3% FC/CYA ratio I'm saying you could do if you had supplemental algae prevention has the same active chlorine level as around 0.01 ppm FC with no CYA so extraordinarily low. There's no way commercial/public pools would go for this because they want to have a certain minimum kill rate of pathogens to prevent person-to-person transmission of disease and they need higher levels of oxidation due to higher bather loads (and most such pools don't have supplemental oxidation systems), but in a residential pool that risk is very low. Also, the systems used with DIN 19643 to maintain low chlorine levels are very high end with fast turnovers and very responsive dosing systems. You don't have anything like that in your own pool which is why you probably should not try and go below 1 ppm FC even if you had lower CYA levels (which you wouldn't since you want a lower active chlorine level so lower FC/CYA ratio).

[radante]

Chem Geek, if I don't plan on using stablized tablets, would I need to worry about the ratio...for, where would the CYA come from? Can one just use bleach as their daily and/or weekly disinfectant...all while monitoring the active chlorine levels during the day so as to make sure it does not get too low?

[radante]

Chem Geek, if I don't plan on using stablized tablets, would I need to worry about the ratio...for, where would the CYA come from? Can one just use bleach as their daily and/or weekly disinfectant...all while monitoring the active chlorine levels during the day so as to make sure it does not get too low?

Chem Geek, if I don't plan on using stablized tablets, would I need to worry about the ratio...for, where would the CYA come from? Can one just use bleach as their daily and/or weekly disinfectant...all while monitoring the active chlorine levels during the day so as to make sure it does not get too low?

Also, it is a vinyl pool so I'm not too worried about the copper sulfate staining.

[chem geek]

If you don't use any CYA at all, not even adding pure CYA initially, then the chlorine will be MUCH too strong and also it will break down MUCH too quickly in sunlight, losing roughly half every hour in direct noontime sun. CYA significantly moderates chlorine's strength and that's a GOOD thing if done in moderation.

I think you still aren't understanding how CYA moderates chlorine's strength. It's not just a little. When I wrote that you would have 0.01 ppm FC with no CYA equivalent of active chlorine in the pool when you have 2-3% FC/CYA ratio, I meant it. So for you to think that you could have 0.5 ppm FC with no CYA in the pool as being OK is strange since that is 50 times higher in active chlorine that oxidizes swimsuits, skin, and hair and produces chlorinated disinfection by-products. FIFTY TIMES!

If you maintained an FC/CYA ratio of 7.5%, then you wouldn't need to use any algae prevention supplements at all, no copper or algaecide needed of any kind. It's up to you which way to go, but you definitely want to use some CYA in the water if you're using chlorine.

[radante]

If you don't use any CYA at all, not even adding pure CYA initially, then the chlorine will be MUCH too strong and also it will break down MUCH too quickly in sunlight, losing roughly half every hour in direct noontime sun. CYA significantly moderates chlorine's strength and that's a GOOD thing if done in moderation.

I think you still aren't understanding how CYA moderates chlorine's strength. It's not just a little. When I wrote that you would have 0.01 ppm FC with no CYA equivalent of active chlorine in the pool when you have 2-3% FC/CYA ratio, I meant it. So for you to think that you could have 0.5 ppm FC with no CYA in the pool as being OK is strange since that is 50 times higher in active chlorine that oxidizes swimsuits, skin, and hair and produces chlorinated disinfection by-products. FIFTY TIMES!

If you maintained an FC/CYA ratio of 7.5%, then you wouldn't need to use any algae prevention supplements at all, no copper or algaecide needed of any kind. It's up to you which way to go, but you definitely want to use some CYA in the water if you're using chlorine.

Ok. Got it. Since I'll be using copper sulfate weekly to control algae, a 2% FC/CYA ratio is my goal. So, to add 30 ppm CYA to my 18,000 gallon pool, I calculate that I'd need about 1.68 gallons of pure CYA initially, right? And then I add enough Liquid Chlorine (weekly) to give me FC of 0.6 PPM. I'm not sure how many gallons that will be yet as I just took over this pool and yet haven't tested it.

[radante]

If you don't use any CYA at all, not even adding pure CYA initially, then the chlorine will be MUCH too strong and also it will break down MUCH too quickly in sunlight, losing roughly half every hour in direct noontime sun. CYA significantly moderates chlorine's strength and that's a GOOD thing if done in moderation.

I think you still aren't understanding how CYA moderates chlorine's strength. It's not just a little. When I wrote that you would have 0.01 ppm FC with no CYA equivalent of active chlorine in the pool when you have 2-3% FC/CYA ratio, I meant it. So for you to think that you could have 0.5 ppm FC with no CYA in the pool as being OK is strange since that is 50 times higher in active chlorine that oxidizes swimsuits, skin, and hair and produces chlorinated disinfection by-products. FIFTY TIMES!

If you maintained an FC/CYA ratio of 7.5%, then you wouldn't need to use any algae prevention supplements at all, no copper or algaecide needed of any kind. It's up to you which way to go, but you definitely want to use some CYA in the water if you're using chlorine.

Ok. Got it. Since I'll be using copper sulfate weekly to control algae, a 2% FC/CYA ratio is my goal. So, to add 30 ppm CYA to my 18,000 gallon pool, I calculate that I'd need about 1.68 gallons of pure CYA initially, right? And then I add enough Liquid Chlorine (weekly) to give me FC of 0.6 PPM. I'm not sure how many gallons that will be yet as I just took over this pool and yet haven't tested it.

I just calculated that 400 ml of 10% bleach will raise FC by 0.6... so if I can get the CYA to remain steady at 30PPM, then just 400 ml per day of 10% bleach would achieve the 2% FC/CYA ratio..correct?

[chem geek]

If your pool is exposed to sunlight, then 30 ppm CYA is not going to protect the chlorine very well from breakdown so unless you have a system that is measuring chlorine regularly and dosing regularly then I'd suggest going higher to at least 50 ppm and then use at least 1 ppm FC. At 30 ppm CYA you will probably lose half or more of your FC in a day while at 50 ppm CYA you'll probably lose less than one-third so might be able to go from 1.5 ppm FC to no lower than 1.0 ppm FC by the next day.

You can use PoolMath to calculate dosages and it weight of pure CYA since it's not a liquid. It dissolves slowly so it's easier to put into a sock or old T-shirt in the skimmer of hanging over a return flow to get it dissolved in about a day.

[radante]

Just an update, ChemGeek. Finally got the K-2006 test kit in. Having a hard time keeping CYA up above 30PPM. I tried a liquid form of CYA, might have to take the slow dissolve sock approach. My FC was 3PPM three days ago and is now 1PPM...so the CYA seems to be protecting the chlorine fairly well, despite likely being under 30PPM at the moment. CC is 0.5PPM. Since I'm using Copper Sulfate for my algae control, my PH was initially 8, then I added some muriatic to bring it down. CC has been 0.6 and 0.5 past few days...is shocking the pool the only way to bring it down to 0 in between bathers?

[chem geek]

Though you could elevate the chlorine level to try and get rid of the CC, the easiest way is usually just to uncover the pool and expose it to sunlight. However, you shouldn't normally be having CC in the pool. I usually measure <= 0.2 ppm CC in my pool (using a 25 ml water sample for the FAS-DPD FC & CC test).

Given your lower chlorine loss rate at low CYA, it may be that your pool doesn't get that much sun, is that right?