Lowering Chlorine

[Maxemily]

Hydrogen peroxide that is.

I will spare you the whiskey induced excessive chlorine level story in my 325 gallon spa except to say the FC was 14 after 24 hours. I looked around this forum and found a blurb about hydrogen peroxide, lowering chlorine, 16 oz, and 10 FC drop. That was all I the persuasion I needed. I poured the 16 oz in the tub and poof! no FC. So, I added Clorox and added Clorox and added Clorox - no FC. Turns out it took 10 additional ounces of bleach to get back to an FC of 2.

If memory serves, the 16 ounces of H2O2 offset 20 ounces of Clorox.

Time to go relax in my experiment. I'll let you know if I have any skin left.

[chem geek]

Hydrogen peroxide that is.

I will spare you the whiskey induced excessive chlorine level story in my 325 gallon spa except to say the FC was 14 after 24 hours. I looked around this forum and found a blurb about hydrogen peroxide, lowering chlorine, 16 oz, and 10 FC drop. That was all I the persuasion I needed. I poured the 16 oz in the tub and poof! no FC. So, I added Clorox and added Clorox and added Clorox - no FC. Turns out it took 10 additional ounces of bleach to get back to an FC of 2.

If memory serves, the 16 ounces of H2O2 offset 20 ounces of Clorox.

Time to go relax in my experiment. I'll let you know if I have any skin left.

As shown in the first part of this post, chlorine oxidized hydrogen peroxide to oxygen gas on a 1:1 molar basis. So the relationship between equivalent bleach and hydrogen peroxide is as follows:

(volume sodium hypochlorite) * (density sodium hypochlorite) * (% weight sodium hypochlorite) / (74.44 g/mole) =

(volume hydrogen peroxide) * (density hydrogen peroxide) * (% weight hydrogen peroxide) / (34.015 g/mole)

The density of 6% bleach is around 1.08 g/ml (12.5% chlorinating liquid is around 1.16 g/ml) while the density of 35% hydrogen peroxide is around 1.13 g/ml (20% hydrogen peroxide is around 1.07 g/ml). So the relationship formula for 6% bleach vs. 35% hydrogen peroxide is:

(volume sodium hypochlorite) / (volume hydrogen peroxide) = (1.13 * 35% / 34.015) / (1.08 * 6% / 74.44) = 13.36

For 3% hydrogen peroxide (with a density of 1.01 g/ml) we would have

(volume sodium hypochlorite) / (volume hydrogen peroxide) = (1.01 * 3% / 34.015) / (1.08 * 6% / 74.44) = 1.02

In your 325 gallon spa, the initial FC was 14 which represents the equivalent of 9.4 fluid ounces of 6% bleach or about the 10 ounces you estimated. You said you added an additional 10 ounces of bleach and ended up with an FC of 2 so the amount of bleach used up is equivalent to around 8.7 fluid ounces so the total bleach is 9.4+8.7 = 18.1 fluid ounces equivalent. Theoretically, the 16 ounces of 3% hydrogen peroxide would require around 16.3 ounces of 6% bleach so this is order-of-magnitude correct.

So the rough rule of thumb is that the volume of 3% hydrogen peroxide needed to neutralize a volume of 6% bleach is roughly equal. Also, in 350 gallons, neutralizing 10 ppm FC requires around 7.1 fluid ounces of 3% hydrogen peroxide.

Am I correct that the hydrogen peroxide you used was 3% in strength? Also, where did you find the blurb about 16 ounces of hydrogen peroxide removing 10 ppm FC? Based on the above, that's not right, if 3% is the assumed strength.

Richard

[Maxemily]

Where were you yesterday!

"...where did you find the blurb about 16 ounces of hydrogen peroxide removing 10 ppm FC?"

Yeah, about that... the aforementioned whiskey might have played a role in my putting two entirely different paragraph together into what I wanted to read.

Yes, it is 3%. Your basic drugstore variety.

"...in 350 gallons, neutralizing 10 ppm FC requires around 7.1 fluid ounces of 3% hydrogen peroxide."

That would be very close to what I experienced.

Thanks for taking the time to sort through the math.

[Dust]

I know it doesn't address your question (Chem Geek already handled that nicely) but I know my spa dealler sells a product called "Spa Boss X-It" that dropped chlorine by 10ppm per 30 grams.

There is no active ingredient on the bottle and it could just be packaged hydrogen peroxide (though it is a powder), but it sure worked nice.