Tracy - sorry about the loss. My 2 cents it was not just or even mostly the aeration. More likely new water and cloudy skies for several days. Doubt it was heat related. With that short a run time increase and no whole pond turnover the HSB would have moved to the part of the pond where DO was higher. Probably running at to high a carrying capacity and whole pond low DO due to new water and cloudy skies. Could easily be wrong though - a guess.