its about 10-15mg per gallon depending on your water supply. i would also use a slice of orange or another type of citrus in a type of a teabag or strainer and let the chlorine and chloramine react with it, then remove it from the water after about 30 minutes...l. this reaction can effectively destroy chlorine and chloramine but will lower ph slightly, less than a fertilizer would. i would also add a few drops per gallon of hydrogen peroxide. if you really want to have a complete reaction i would use fruit, hydrogen peroxide, and Ascorbic acid (vitamin c) and allow 12 hours to mix and catalyze with aeration.