during the summer our waterfall gets ''algae'' on it and looks ratty . during the winter the stuff hardens and peels off leaving pleasant looking stones . i wondered about putting some kind of liquid on it while it looks nice to abate the algae but don't want a detrimental effect on fish and frogs . i suspect it is a bad idea and i'd appreciate any suggestions . it is three tiered waterfall kind if like stair steps and i scrub it during summer with a very stiff brush but it never does look as nice as first thing in spring . as always i appreciate your thoughts . . . peace