Horticultural cornmeal placed in small burlap bags, tied up with string and attached to a stick or even a duck decoy, does not stay on the bottom of the pond! It pops back up and smells grandly when you then pull it out and distribute over the algae. It does seem to sink better then! I'll be watching to see if all the work I did has paid off. I know it won't hurt.

Next time you put the cornmeal in a bag, include a rock to sink & hold it on the bottom. It does have a fine odor!