Sick Mbunu

Sick Mbuna

Work has a 100g mbuna tank, and the largest of the fish (about 6in or so) is showing signs of problems. Can't claim to know much about our cichlid overlords, so hey, I'm asking here.

Water test should be coming tomorrow, I can pretty much guarantee the pH will be around 7.5, they have no buffer of any kind, but this is the first signs of stress in 3 years.

What she's doing: just floating there. Won't move all that much, and tends to tip over a little and then righten itself. Don't see any obvious physical problems except for a couple of tail nibbles, but I'm blaming that on the other fish.

Any ideas? (without knowing specific water parameters?)

It's a true Mbunu, don't know the exact species, but it's a melanchromis, and it's purple... It's also twice as big as any other fish in the tank, save the catfish. A week ago it was the undisputed boss of the tank, and had been for years... in fact, it's the mother of most of the current Mbuna residents.

Ok... the ailing Mbuna has faded in color, gone from bright purple to near-white. the other 6 fish are fine and none are attacking the sick fish.

Did a couple of water tests, pH maxed out on the midrange test (only goes to 7.5), ammonia is nil, nitrates very very barely register.