I throw in the swimming pool chlorine tablets- one (small one) per 150 gallon stock tank. It dissolves slowly so it keeps working for several weeks. Its not stong enough to eliminate all the green (except for right next to it) but it keeps it down enough that I don't have to scrub and clean weekly any more. Clorox is just a short term clean up- it evaporates into the air unlike the pool chlorine.