90 GALLON its been set up for over a year, there is 2 Sun Shines peacocks male/female, 5 zeba Obliquiden 1 male/4females, 5 Hap Ahli, Electric Blue 1 male/4 females, 2 Taiwan Reefs both males, 1 Protomelas sp. "Spilonotus Tanzania" male, 3 flamebacks 1 male/2 females, 3 pleco's and no new fish have been added in a few months, and he doesn't look sick at all.
well, I don't have a lot of experience with haps and peacocks, but it sounds like it could be a stressed fish problem. Have you ever noticed him hiding in the corners? does he try to eat, and then spit it back out?
I do know it is unusual for malawi cichlids of all kinds to not overeat enthusiastically.
you might want to consider checking the nitrate level in your water. Even if you do weekly water changes, over time they can creep up pretty high. Could be a high nitrate problem and he's the first one showing signs of the stress. If so, a large water change, or a couple over the next few weeks should remedy the problem.
You also might want to consider posting in the illness subforum here. Even if he doesn't look sick, a malawi cichlid not eating is a sign that something is amiss.
Good luck. Hopefully others will chime in with some better advice.
Did you change food? Does he mouth and not swallow or simply ignore the food?
Regardless, I will second the large water change - 75%+ to get the nitrates to the 10ppm range and see if clean water helps.
If he doesn't eat for a couple more days with really clean water, I would put him in a hospital tank with lights out and see if he will take food there after a couple of days - to determine if it is stress from other fish or not.
He still doesn't eat after a couple more days and shows nothing else, I would try to treat him with metronidazole in the hospital tank as it is relatively mild and very effective on bloat.
After that I would assume he should be getting better or showing other symptoms.