we have had green water ALL summer and can not see our fish also have found two of the comets dead and with no marks on them . put ''api algaefix'' in pond every 3 days 13 times and another nine times from new bottle with barely noticable results . also tried another water clarifier with zero results . pond is about 2500 gallons with filter and water fall and for past 10+ years has been mostly crystal clear . any thoughts appreciated , i think . . . peace....PS . it does seem to have deterred the heron .