okay so about three days ago my fish have started to just be really lazy. they dont eat as much. and the top of my water is getting all oily and my discus have been seeming to start shedding their skin.umm not really to sure what to do right now but try and not kill my fish i was thinking to pull them all out into a small tank...umm anyone have any ideas.. or might be able to contruibute to save my fish. and one of them are getting a little dark...this all started happening after i brought a new discus into the tank. and the new discus is doing just fine and the other 3 i have in my tank not so well.