aggressive guppy

So I’ve got a 29 gallon tank that’s divided in half. On one side I have my male guppies and the other my female. Anyway, I have one of the male guppies in an isolation box because he kept endlessly harassing a single other male guppy. The isolation box is mesh so it just sits in the main tank...

I've had a guppy and a cremesicle Lyretail Molly for quite some time, and the guppy has always enjoyed playfully chasing the molly around the tank. This morning, however, I guess he was hungry, as he decided to nip at the Molly until the poor guy had several red spots on him. As soon as I fed...