I read somwhere it was one tablespoon per thousand gallons. If you put too much it does not hurt anything as it does not change the p.h.
When I added too much it coagulated evertything on the surface, when you use the right amount it settles to the bottom. It was unnettable from the top, except when I added hay to the net to give it something to cling to. With the right amount you can stir the pond to have the settlements end up in the deeper middle.
Good luck!