18" is the visibility most people are trying to attain by adding nutrients. The green "muck" floating in your pond is minnow and bluegill food. If you clear up your pond it will cut down on your number of fish. By areating at the bottom of the pond you are disturbing the bottom sediments, which are probably very fertile, and fertelizing your bloom. If you continue on this path eventualy you should reach a natrual equalibrium where you stir up as many nutrients as are consumed. But if you want clear water now, despite the side effects, you may be better off not arreating.
Also rooted plants compete with algae for nutrients. Try adding water lillys and encouraging plant growth.