I've had the same problem. I got a german blue ran about 2 weeks ago and it was fine. I also have a bolivian ram, both about the same size. I noticed, about 3-4 days ago, that the blue had vanished. No trace, at all. I've looked thru all my plans and in the decor that it could hide, nothing. No carcus, no remains of ANY kind, and its to big to get sucked into the filter.