I agree about the bloom. I go past our local hospital several times a week and it drives me crazy. They have a number of beautiful ponds -- and golf-course quality lawns. More than likely all of the fertilizer that is keeping the grass beautiful is keeping the pond very green, and frequently full of filamentous algae. The only real way to control this is to limit the fertilizer runoff into the pond, or to get lots of plants in the pond to take up the fertilizer nutrients.
Try adding a bunch of inert substrate to produce the bio film to eat up all the excessive nutrients. Feeds the fish then start culling them like crazy.
