BlueSpa Posted January 24, 2009 Report Share Posted January 24, 2009 Any suggestions for lowering the FC levels after superchlorinating?? After our refill yesterday I added Dichlor to superchlorinate and activate the N2 cartridge per the N2 instructions. Had the cover open and the jets on for a while to off-gas. But today is a cold, cloudy day and our FC levels are in the 15ppm range. A little too cold and windy to leave the cover open if there is any way to avoid it. With a clean system I'd imagine it'll take a while for the chlorine levels to come down. Any suggestions for getting the FC down around 5ppm so we can soak tonight?? The new water looks very inviting!! Quote Link to comment Share on other sites More sharing options...
BlueSpa Posted January 25, 2009 Author Report Share Posted January 25, 2009 Any suggestions for lowering the FC levels after superchlorinating?? After our refill yesterday I added Dichlor to superchlorinate and activate the N2 cartridge per the N2 instructions. Had the cover open and the jets on for a while to off-gas. But today is a cold, cloudy day and our FC levels are in the 15ppm range. A little too cold and windy to leave the cover open if there is any way to avoid it. With a clean system I'd imagine it'll take a while for the chlorine levels to come down. Any suggestions for getting the FC down around 5ppm so we can soak tonight?? The new water looks very inviting!! For those that are interested, searching "chlorine neutralizer" will bring up some suggestions, one of which is sodium thiosulfate. (I was searching but hadn't thought about using the term neutralize). Also regular hydrogen peroxide came up as working somewhat, 16oz would reduce the 10ppm Cl, but I wasn't sure of any byproducts of adding so will just wait for the Cl levels to come down on their own. Barb Quote Link to comment Share on other sites More sharing options...
chem geek Posted January 25, 2009 Report Share Posted January 25, 2009 Barb, Most chlorine neutralizer products for pools are sodium thiosulfate. The specific dosage depends on whether the sodium thiosulfate is anhydrous or pentahydrate. The latter is more common and typical dosing is 2.4 ounces weight per 10,000 gallons for 1 ppm (theory says it should be more like 2.0 ounces so not sure why the dosing instructions are off a bit assuming the product is pure). This is 0.084 ounces weight in 350 gallons for each ppm reduction. Assuming 1.7 g/ml density, this is about 0.3 teaspoon. So to reduce FC by 10 ppm in 350 gallons, this is about 3 teaspoons. I suspect this is going to be approximate. Hydrogen Peroxide would oxidize chlorine to chlorate so isn't good to use as a chlorine neutralizer. [EDIT] I'm wrong about this -- hydrogen peroxide is more likely to get oxidized by chlorine to produce oxygen so isn't bad. [END-EDIT] Almost all chlorine neutralizer you will find will be sodium thiosulfate, though some is sodium sulfite. Richard Quote Link to comment Share on other sites More sharing options...
BlueSpa Posted January 26, 2009 Author Report Share Posted January 26, 2009 Barb, Most chlorine neutralizer products for pools are sodium thiosulfate. The specific dosage depends on whether the sodium thiosulfate is anhydrous or pentahydrate. The latter is more common and typical dosing is 2.4 ounces weight per 10,000 gallons for 1 ppm (theory says it should be more like 2.0 ounces so not sure why the dosing instructions are off a bit assuming the product is pure). This is 0.084 ounces weight in 350 gallons for each ppm reduction. Assuming 1.7 g/ml density, this is about 0.3 teaspoon. So to reduce FC by 10 ppm in 350 gallons, this is about 3 teaspoons. I suspect this is going to be approximate. Hydrogen Peroxide would oxidize chlorine to chlorate so isn't good to use as a chlorine neutralizer. Almost all chlorine neutralizer you will find will be sodium thiosulfate, though some is sodium sulfite. Richard Thanks Richard! Looks like I'll be heading out tomorrow for some sodium thiosulfate - didn't think I'd need to but I'm missing the nightly soaks after only 3 nights!!! (Plus we're due for some snow which will be perfect with the new water, glass of wine, etc.) Quote Link to comment Share on other sites More sharing options...
chem geek Posted January 26, 2009 Report Share Posted January 26, 2009 Barb, I was wrong about what I said about Hydrogen Peroxide (I corrected and edited my post above). At pool pH, it's more likely for chlorine to oxidize hydrogen peroxide to oxygen than for hydrogen peroxide to oxidize chlorine to chlorate. In chemistry, the following is more likely to occur: OCl- + H2O + 2e- ---> Cl- + 2OH- ..... EO = +0.81V H2O2 + 2OH- ---> O2(g) + 2H2O + 2e- ..... EO = +0.146V ----------------------------------------------------------------------------------------------------------------------------------------------------------- OCl- + H2O2 ---> Cl- + O2(g) + H2O .... EO = +0.956V Hypochlorite Ion + Hydrogen Peroxide ---> Chloride Ion + Oxygen Gas + Water than the following: HOCl + H2O ---> HClO2 + 2H+ + 2e- ..... EO = -1.645V H2O2 + 2H+ + 2e- ---> 2H2O ..... EO = +1.776V ------------------------------------------------------------------------------------------------------------------------------------- HOCl + H2O2 ---> HClO2 + H2O ..... EO = +0.131V Hypochlorous Acid + Hydrogen Peroxide ---> Chlorous Acid + Water HClO2 ---> H+ + ClO2- Chlorous Acid ---> Hydrogen Ion + Chlorite Ion OCl- + H2O + 2e- ---> Cl- + 2OH- ..... EO = +0.81V ClO2- + 2OH- ---> ClO3- + H2O + 2e- ..... EO = -0.33V ---------------------------------------------------------------------------------------------------------------------------------------------------------------- OCl- + ClO2- ---> Cl- + ClO3- ..... EO = +0.48V Hypochlorite Ion + Chlorite Ion ---> Chloride Ion + Chlorate Ion Though the above refers to thermodynamic tendency, the rates are such that chlorine will tend to oxidize hydrogen peroxide to oxygen gas. At low pH, there is more hypochlorous acid than hypochlorite ion so the tendency to produce chlorous acid increases, but at pool/spa pH (i.e. around 7.5), it's more likely for chlorine to oxidize hydrogen peroxide to oxygen gas. The amount of hydrogen peroxide it takes to neutralize chlorine depends on the strength of the hydrogen peroxide. In 350 gallons, 16 ounces of hydrogen peroxide eliminating 10 ppm chlorine implies a strength of hydrogen peroxide of around 22%. So you could use hydrogen peroxide to lower chlorine levels if you wanted to, though it is more common to use sodium thiosulfate as the chlorine neutralizer. To minimize any byproducts, you want the pH to be normal-to-high so 7.5 or higher instead of on the low side closer to 7.0. Sorry I didn't get this right the first time. Richard Quote Link to comment Share on other sites More sharing options...
BlueSpa Posted January 27, 2009 Author Report Share Posted January 27, 2009 So you could use hydrogen peroxide to lower chlorine levels if you wanted to, though it is more common to use sodium thiosulfate as the chlorine neutralizer. To minimize any byproducts, you want the pH to be normal-to-high so 7.5 or higher instead of on the low side closer to 7.0. Thanks so much for taking the time to explain and correct this!! I wasn't able to find any sodium thiosulfate today so may give the peroxide a try. I just tested the water and our FC is still a bit too high at 8ppm, and our pH is around 7.7 so should work fine and I'm sure I have some peroxide around here. Should be enough to get it closer to 5ppm. Maybe we'll be tubbing in the snow tomorrow after all!! Quote Link to comment Share on other sites More sharing options...
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