Thanks for reply. They were intially fish that we bought and put in a starter bowl (which is tiny), they didnt have a filter or anything. They grew and became a bit big for the round bowl, so we got a glass tank. The tank measures 29.5Lx 32Hx 18.5D. Before we moved them I conditioned the water. Im not so clued up on the parameters. Could the big one be bullying the little one coz of the new environment? When i feed them they both eat and the big one sort of refrains from chasing the little one, once he's done he'll chase her again. He seems to nudge and 'nip' under her belly and yes, she does go and hide in the corner or behind the plant. He'll still go to her and push her out of where she's hiding. She seems ok ie fins dont seem damaged. We did seperate then yesterday for a while, and they both seemd a bit frantic. The little one seem to not settle down, kept swimming around like when they see its feeding time. The little one does seem round, right back until where the back tail starts.