well i have gravel now, if i put in a shrimp pellet in the tank it will sit on the bottom until someone bits it, once they take a a bit the small peaces slowly rise to the top. I have even had a few pellets that wouldn't sink right away. I have been thinking about sound for weeks now.
My sump feeds from about 2 inches bellow the water, and the return is about 1 inch bellow the water line, however its spraying down at a 45 degree angle. then on the other side of the tank I have a fluval 403 feeding from about 2 inches above the bottom and returning 1 inch bellow the water. The current is strong enough it create mini whirlpools in the middle of the tank.If I drop a pellet at the end of the tank where the sump returns it will fly across the tank unit it get to the other side where it slowly drift upwards once some one bits on it. After changing the flow pattern I no longer see any poop on the bottom