About a week ago, I got 5 glass catfish. From the moment I put them in, one of them stays behind the filter and I’ve only ever seen him one time. I noticed a day ago that one of my catfish was missing his tail and another one looks like he’s being nipped on the tail. They are in there with guppies and one 1 1/2 inch rainbow shark but it’s really a mellow tank. They don’t show any signs on fin rot so I’m not sure. The catfish that is missing his tail is starting to turn a milky white color where his tail is missing and looks like it has spread or the spot has gotten bigger since then and now he’s laying at the bottom of the tank is there anything I can do?