Hello, i have a dwarf gourami (male) in a 20 gal tank. he is about 2.5 inches. I just put a female dwarf gourami in the tank today. She is about 1.25 inches. He is viciously nipping her tail fin. He will follow her, curve his body, then snap out and bite her. Is this normal? right now i put him in an iso tank in fear of him killing her. He has been nipping at the tail of a guppy in the tank every now and again but nothing this vicious. Any thoughts?