dude, i work at a pool store. The correct way to do it is read the label ( this is also true for many other things). Im trying to see the percentage of sodium bisulfate... looks like its ninety- something, so thats good. Now, on the label, should have a table as to how much to use to drop the ph of your pool. It works the same way for all water, so do the math, it shouldnt b that difficult.