Cecil's advice is the best for the short term situation. Surface aeration is the cure for what ails you. You probably won't have a DO problem until your visibility gets down to less than 12" but be ready before this happens. I had this happen to me on a 1.1 ac pond in south Louisiana that has 5 acres of runoff into it. The danger is when the bloom gets dense and then you get 1-2 days with heavy cloud coverage. You won't know what hit you. I now have a 3/4 hp surface aerator in place with a timer set from 4-8 AM during the hot summer months. For immediate relief a 2" jagger/trash pump choked down to a 1" discharge against solid or slat wood surface before it falls into the pond will create some 0xygen. Time to start shopping for a surface aerator. Mine was about $800. It is 220 v and hopefully will last many years.