I am not a Marine Biologist, but there is a good chance it is cichild bloat.
If it is.. Here are some things I recommend..
Step 1
Quarantine the fish if possible. One of the leading hunches is that a parasite causes it. If you only have a single sick fish, move it to a quarantine tank for treatment. If several fish show symptoms, perform your treatment in the main tank.
Step 2
Perform a water change. Whatever the cause of cichlid bloat, improved water conditions will help your fish. Change 30 percent of the water with a bucket and aquarium siphon.
Step 3
Remove carbon and zeolite filter media. Many aquarium filters contain inserts that absorb harmful chemicals. Unfortunately, they also absorb medications. Remove any filter inserts or cartridges that contain activated carbon or zeolite. Replace them in case they contain a parasite.
Step 4
Add Epsom salt to the water. It will raise the pH, simulating the water conditions your African cichilds are used to. Around 1 milliliter of it per 10 liters is the right amount.
Step 5
Medicate the tank. Anecdotal evidence suggests that Metronidazole and Clout can effectively treat cichlid bloat.
