Eating fish poo!?
If you have enough filtration then you shouldn't have fish poo anywhere in the tank, unless you have some dead spots in which case you should reconsider your layout.
If you are looking for an L-Number then you need to be careful as most only tolerate soft acidic water, whereas your cichlds should be in hard alkaline water.
A bristlenose is the most commonly used L-Number in these circumstances but there are one or two others that are suitable, but I am not sure what your motivation is behind having one. They wont eat poo as far as I know and if thats why you want one then I would address your filtration / layout first.