Even though these aren't considered true earth eaters, the Andinoacara below and many Central and South American cichlids spend a lot of time digging for small edibles,
So traditionally thought of "bottom feeders" are really not necessary.
And these cichlids(even though they, and their mouths are fairly large), prefer to eat smaller size chunks, larval snails and mollucs in nature, and expel non-edible particles through gill openings.
Big chunks of gravel, or large pellets if swallowed whole can often cause blockages, or hurt gill membranes.
I have had 10" Geophagines prefer tiny pellets and even flake food, compared to even medium size pellets