You know, maybe it is a coincidence, but the algae started getting worse about 2 yrs after I got the grass carp. There are about 20 or so very large ones now (about 12-15 lbs). Will plan to remove them and clean any dead algae after I drain. Will spray with the Cutrine plus. Don't know about the Tilapia - will have to look into that. Thanks for all the input. That will help me get started and hopefully I can get a handle on this.