i wouldn't separate the fish if the only thing you see is a small wound. it is stressful to the fish to separate it from it's normal living space. is the wound looking any better? i didn't ask but i assume that your tank is cycled and all your water parameters are correct. do you have a liquid test kit? could you post your ammonia, ph nitrites and nitrates? if they are all within normal limits and the other fish aren't picking on the injured one, i would watch for signs that the wound is healing and not getting any worse. if you must medicate the fish then i would remove to another aquarium or bowl to treat. i wouldn't treat all my fish for just the one that has the problem. do the other fish all seem healthy?