# Thread: Hydrogen peroxide to lower FC.

1. ## Hydrogen peroxide to lower FC.

I have 2 pools that had high FC, and recalled reading about hydrogen peroxide to reduce FC. Normally I would just turn off the chlorinator and let the FC come down naturally but the water is cold, there's not much sun around and I found some cheap hydrogen peroxide by chance and thought I would share my results.

From a quick search I found this quote;
"27% hydrogen peroxide at a reasonable price of \$17 per gallon. It would only take 115 fluid ounces (around 3-1/2 quarts so somewhat less than one gallon) to lower the chlorine by 50 ppm in 10,000 gallons."

With that as a starting point and using Google to convert to metric and then adjusting for my pool I get; 1,040ml of 27% H2O2 in 29,000L to lower FC by 20ppm.

As luck had it I found 5 litres of 190g/L or 19%w/v hydrogen peroxide for \$10, a cancelled order. Adjusting for 19% I get; 1,540ml of 19% H2O2 in 29,000L to lower FC by 20ppm.

I don't know where I went wrong but my observed results are out by a factor of 2.
Day 1: FC = 25. + 1,500ml 19%H2O2 + 1.5hrs Cl2 run time + 24hrs. FC = 15.
Day 2: FC = 15. + 1,500ml 19%H2O2 + 1.5hrs Cl2 run time + 24hrs. FC = 5.

In reality it was 1.5L of 19% H2O2 in 29,000L to lower FC by 10ppm.
Or, 530ml of 19% H2O2 in 10,000L to lower FC by 10ppm.
Or 68 fluid ounces of 19% H2O2 in 10,000 gallons to lower FC by 10ppm.

2. ## Re: Hydrogen peroxide to lower FC.

The quick and dirty rule of thumb is this - the amount in oz of 6% bleach it takes to raise your FC by X ppm's is equal to the amount of 3% H2O2 needed to lower the FC by X ppm's. That rule of thumb is good to use because it's a lot easier to find 3% peroxide in a drug store and most people use peroxide as an FC lowering chemical in spas where the water volumes are A LOT lower.

3. ## Re: Hydrogen peroxide to lower FC.

I used yellow gone a couple of time to lower my FC when I got my SWG and was testing the setting. use it wisely though because it will eat up all your FC pretty quickly if you put too much of it in your pool. it will also lower your PH in the process.

4. ## Re: Hydrogen peroxide to lower FC.

Originally Posted by misteur G
I used yellow gone a couple of time to lower my FC when I got my SWG and was testing the setting. use it wisely though because it will eat up all your FC pretty quickly if you put too much of it in your pool. it will also lower your PH in the process.
That's an EDTA/Ammonium Sulfate based chemical. It's meant to work as an algaecide by the in-situ formation of monochloramine which is a powerful algaestat. But it does so by consuming FC in the process. A lot of FC!

Peroxide is probably the least harmful choice, it simply annihilates itself with chlorine and forms oxygen gas, chloride and excess HCl.

5. ## Re: Hydrogen peroxide to lower FC.

Originally Posted by JoyfulNoise
The quick and dirty rule of thumb is this - the amount in oz of 6% bleach it takes to raise your FC by X ppm's is equal to the amount of 3% H2O2 needed to lower the FC by X ppm's. That rule of thumb is good to use because it's a lot easier to find 3% peroxide in a drug store and most people use peroxide as an FC lowering chemical in spas where the water volumes are A LOT lower.
Thanks Matt,
I did see something similar but in honesty didn't really give much thought to either thinking it would be to costly to use any form of peroxide hear. It was by shear chance I found the 'Spa Protector' product for \$10, a quick search reviels it normally retails for closer to \$50 and for \$50 I would have abandoned the idea. For \$10 it was a bit an experiment and allowed me to lower the FC in one of my pools before replacing the seals in the filter.

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