African Cichlid swimming erratically

Question
Hi! We have a 29 gal tank with 10 young African cichlids. It has been set up for approx. 2 months. The ph is 7.0 and all of the fish seem perfectly healthy except for one larger yellow cichlid. For the past 2 days, he acts as if he is trying to shake something off: He shakes back and forth rapidly almost constantly. He will still eat fiercely, then return to the bottom portion of the tank, usually in a corner, and resume shaking. He also mouths the glass occasionally while shaking. The other fish don't avoid him but don't take any interest in him: They merely act as if he weren't there. He will occasionally act aggressively toward other fish by chasing them off. He does not appear to have any signs of disease but his coloration has gotten darker and he keeps his fins laid down. We did a 25% water change 7 days ago when we removed two convict cichlids and their fry. We added two new fish yesterday, but he had already started his behavior. Please help if you can! Thanks, Lori

Answer
Hi Lori,
While usually this would be a cause for concern. If you water tests turn out good with ZERO for ammonia and nitrite and low nitrate, then another possible reason is your cichlid is actually displaying a territorial or courtship behavior. If you don't see any signs of parasites (shine a flashlight on him to see if a golden overcast is present which would indicate velvet) I'd suspect that's what it is instead is a normal behavior, I've read of other people having the same problems and it turned out to be nothing.

I hope this helps and best of luck!
Karen~