# Thread: Pool math chlorine question

1. ## Pool math chlorine question

When I enter 8% chlorine into the FC table the calculator it reads "Weight", however when I enter 12.5% the word changes to "Trade". Just wondering what the difference is and why that difference is noted?

Rolo

2. ## Re: Pool math chlorine question

Bleach sold for laundry use is sold by weight percent of sodium hypochlorite. That's 6% and 8.25%.

Liquid chlorine sold for pools is typically listed as Trade % which is really a volume %. That covers 10%, 12.5% & 15%.

The difference between weight and volume percent have to do with the specific gravity of the solution. It changes the FC calculations slightly.

3. ## Re: Pool math chlorine question

That is very helpful, JoyfulNoise. Thank you. I didn't realize that the laundry version was listed as weight %.

I just got a quote from a chemical supplier for 12.5% Sodium Hypochlorite. 12.5% by weight is 15% by volume.

4. ## Re: Pool math chlorine question

Interesting. So the 8.3% great value bleach at walmart is actually probably a higher percentage of sodium hypochlorite than the 10% liquid chlorine they were selling in the pool section for a while. That would explain why when I switched from the liquid chlorine stuff to the laundry aisle stuff, I didn't have to alter the timing on my stenner to meet my target FC level, even though going from 10% to 8.3% made me think I should have had to use more.

5. ## Re: Pool math chlorine question

1.45 oz 8.25% provides the same amount of chlorine as 1.16 oz of 10% or 1 oz of 12.5%.

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