Sorry bud, it sucks, had that happen today as well. I have a 55g Mbuna tank with about 13 mubuna and 5 cats in it. I bought a 4"+ yellow lab on Monday and added to the tank to try to get the other 3 Y.lbs in there to breed...today, he was found Dead. Yet I added a unknown cichlid I got from Scott here on MCA 2 weeks ago which was only half the labs size...he's still perfectly fine, they don't give him a second look. Weird how these fish act at times man.