TB,proper aeration will reduce your nutrient load but as you are fertilizing for a bloom you may find your current fertilizer rates dont apply. Aerating to reduce or elminate algae may leave you dissapointed. Aerate to promote aerobic bacteria, aerate to provide your fish with the entire pond to live. (no thermal barrier) and aerate to promote all around fish health. The additional benefits of proper aeration are endless.Sunight, water,and nutrients of any amount will always produce some algae.Since your pond is only 4 years old your BOD is still on the increase. Your deepest areas are acting as a sediment bowl and you may want to correct things soon. Switching to all catfish and having an aerator may leave your water very cloudy which would slow the chance for excessive algae. As far as cost look at the specs on a Vertex Air 1 (click on homepage) Good Luck Ted