I have tried cornmeal in a 1/4 acre pond and had good results early in the Spring before I discontinued use. I believe the stuff works like barley straw in that it harbors particular types of bacteria that seem to tie up phorphorous in the water column. My only concern is the application mess, the availability, cost, and addition of organic matter.

I would consider a microbial agent, combined with limited amounts of barley rolls around the shoreline for a long term control. Good luck!

It's ALL about the fish!