I have a 30 gal tank sparsly populated with 2 molly-1f,1m. 4 platy-2m,2f. 4 neon tetra. 6 platy fry. Heavily planted. None recently added. One of my male platys was not mature when he was added to the tank with a couple females and a mature male. I actually thought he was a female. He has since matured, and the older male has been attacking him brutally. The young male is starting to fight back, but is still much smaller than the other and is getting the ^&* beat out of him. I'm afraid he will be killed. Any advice?