Cowpuncher, I don't think he was referring to a galvanized water trough. (might be wrong about that). Most of the "tanks" down here are really small ponds from 1/3 acre to maybe 3 acres or so. The copper sulphate will work but he mght need a whole lot of it. Another option is to dig out the shallows. A 1' drop to 3' horizontal is a good slope to prevent growth. A 1' drop to 2' horizontal is even better. Deeper water helps to prevent algae. On a galvanized tank, I've heard of people painting the interior black and it's seems to help retard algae growth. The there's the option of adding the green or blue dye to the water which prevents a lot of the sunlight from hitting the bottom thus preventing algae growth.