how big is the tank? are there other fish in there besides the platies? you might want to introduce a big but docile fish to the tank if you have room, it could cause him to think twice about going after the others (aggressive fish tend to calm down if they don't see themselves as the "alpha" of the tank)
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)