I understand,...I think you need to attack mechanically some how. The gravel size is fine line to get the balance,....no sandstorm vs. no food trapping. A finer sand the fish will continue eating what might bet laying on the surface that they can see. Now some wrasses will root through the substrate,...good and bad. I use to have some large puffers...nice fish, but real pigs. They would take silversides out of my hand, chew them up spit it out, repeat 4 or 5 times, most of the silversides would end up in the gravel. Dam things were always hungry because they spit 1/2 of their meal out. Guess the type of fish you choose comes into play also.