I wound up putting seven 3-4" HBG in the tank, and the tilapia immediately began attacking them. I got after Tillie with my little net and took her right out of there. She's now in a plastic 55 gallon water barrel in the greenhouse.
The best I understand about tilapia is that they are very protective of their territory. But even the related tropical cichlids they sell at Walmart are labeled "aggressive" fish.
