I purchased a group of 16 P. Phenochilus "tanzania" juvenilles at the fall '13 MCA auction. I have kept them mostly in a 75 gallon with other non-aggressive haplochromis-type grow-outs since then. For the first few months they seemed very healthy. Eating New Life Spectrum (NLS) pellets vigorously off the surface.
Early this spring I added a dozen or so A. baenchi - peacock juvenilles - to the tank. In April my first phenochilus died. It looked, for lack of a better term, like a runt; thin with a concave belly. In the next month I lost almost half of them, down to 9 remaining fish. There were no signs of aggression whatsoever.
2 weeks ago I moved the 9 fish to an otherwise empty 40 gallon breeder thinking that maybe they were too stressed in a mixed-species tank. They seem to be behaving normally, no stress, but I still don't see them eating. They seem to be getting thinner and thinner. Last week I lost another. I now have 8 fish left.
Water conditions are decent: pH: 8.0, NH3: 0.0, NO2: 0.0, NO3: 5-10 ppm. At feeding time I see them mouth food like they are hungry, but spit it right back out. Right now I'm feeding only NLS "Cichlid" and NLS "Thera A" pellets, but I'm wondering if maybe I should try some frozen brine shrimp or maybe something else? I have a lot of cichlid experience, but I don't remember ever seeing something like this before. Anyone got any ideas?