Hi!
Can you post your water readings please? NH3, NO2, NO3
pH, gH and kH and temperature too.
With the food advised by members here then there should be no problem with food.
If the water readings are okay too then there's only 1 possibility. The fish is stressed and there're not enough cave/hiding place.
From the pic I could tell that he's a male Pseu.Saulosi and he's not blue means he has been pinned down by the dominant male, he seems to digged that area to make a temporary home. Does your tank has enough cave per fish? It's very essential to have enough cave for every fish in Mbuna tank.