Naughty fish!

My fancy coldwater tank isnt doing too well at the moment. I lost a lovely calico fantail with big eyes. He has had sb issues and he just didnt get better. I took him out the main tank as the others were pushing him about, so he spent the last week in a qt tank but he died this morning. Also my black moor is going the same way. He was ok in the tank keeping out the way but the others spotted him and started pushing him about. (I think they go for their slime coat) My little chocolate oranda cant cope with the big tank so she has a small tank with a filter, and is quite happy. However, today I couldnt stand to see the black moor getting shoved about so I put him in the orandas tank, and thought the chocolate oranda would be ok in the big tank. No way, have had to take her out as well so she is in another qt tank and looks really miserable now. Talk about getting in a mess!