Thanks Micky1, I think that might be the only solution. The situation has worsened, one of the lovely big ones was looking decidely the worse for wear this morning, his tail has been badly nibbled! So we have moved him out & hope he will be OK - he's back with his big buddies. We think he got exhausted trying to keep swimming away from the little fellows (there only seem to be a couple indulging in this cannibalistic behaviour). So we'll take your advice and remove the little troublemakers & put them in an indoor tank, that way they can eat each other if they like! We don't want the other fish picking up on this behaviour either, so it will be good to remove them. Happy New Year to everyone!