As the pond ages and the nutrient inflow remains steady expect the algae to progressively get worse. The next downhill step will be appearence of duckweed/water meal. Both indicators of further eutrophication and enrichment. Aeration will be helpful in minimizing fish kills (summer&winter), although with the pasture nutrient/fertilizer runoff don't it expect it to do much in reducing FA growth.
Read through some of these posts both electric and windmill aeration for background information.
http://forums.pondboss.com/ubbthreads.php?ubb=cfrm&c=6IMO removing the flathead was a wise move and not-so-wise in adding it. They eat too many bass.
