1. ## Pool Math Calculator

I never noticed this before, probably because I always used liquid chlorine and thus entered in 12.5% in the calculator when calculating FC, but why does it say "trade" when you enter say 12.5% for example (for FC) in the calculator next to the percentage, but if you enter 8.25% it says "weight."

2. ## Re: Pool Math Calculator

That feature is new this week.

There are several different standards for measuring the concentration of bleach. Household bleach sold in grocery stores is sold by weight percentage (typically 2% to 8.25%), while liquid chlorine sold by pool stores and cleaning supply stores (typically 10% to 15%) is sold by trade percentage. The two numbers, weight and trade, are fairly close together, but differ just a little because they are based on different historical ways of measuring concentration. I recently updated PoolMath to distinguish between them so it would have better accuracy for higher concentrations of chlorine.

3. ## Re: Pool Math Calculator

That's what I thought - Thanks for the explanation.

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