If you google this question or if you look at the instructions for some calcium chloride packages you will get the standard answer that seems most common, which is about 1.25 lbs to raise 10 ppm in 10,000 gallons. Some other sources say 1 - 1.25 lbs to raise 10 in 10k. Pool Math http://www.troublefreepool.com/calc.html says exactly 15 oz to raise 10 in 10k. Why the difference? Does it depend on other factors or what kind of cal-chlor you buy?