Hey everyone! I know this site has a great calculator to determine how much chlorine to add to achieve a desired PPM, but I'd like to be able to calculate the same result by hand. According to Wiki (https://en.wikipedia.org/wiki/Parts-per_notation), .0001% = 1 PPM. Therefore, if I have 1,000 gallons (128,000 ounces) and add 1 TBSP (.5 ounce) of pure chlorine (as in 100% bleach, which I know doesn't exist publicly, just using it for easy calculations for now), I get 3.9 PPM (.5 divided by 128,000.5 = .0000039). If I input the same values, the calculator agrees perfectly.

However, if we up the values significantly, the calculator no longer agrees. For example: With 50,000 gallons, to get to 4 PPM the calculator determines 25 ounces of pure chlorine. However, hand calculating is as follows: 50,000 gallons = 6,400,000 ounces. Add the 25 ounces for 6,400,025 total ounces. 25 divided by 6,400,025 = .0000039, or 3.9 PPM, not 4 PPM. Just to make sure the calculation simply doesn't include the added 25 ounces, 25 divided by 6,400,000 also equals 3.9 PPM. At first I thought maybe the calculator just rounded, but changing the desired level in the calculator to 3.9 changes the required ounces to 24. So, it's apparent I'm missing something here...

Also, if that question can be answered, I haven't worked the math on substituting pure chlorine for the regularly available 5%, 6%, or 8.25% if anyone has a formula for that.

As a final FYI, the only reason I'm trying to figure this out is to preserve the formula for occasions where technology is not readily available, such as natural disasters or winter storms. I know the page can be downloaded to the local computer, but if the power is out, it doesn't do much good.

Thanks!

Cam