I had 2 mated engineering gobies about 8" each in a former 46ga reef tank. They moved that sand around!!!!
They generally lived in a cave in the LR
, but regularly came out with mouthfuls of sand. They also create crevices between rocks to move the sand around. Any corals on the sand were buried regularly so I had to move them up on the LR
, but the gobies regularly swam to the surface with mouthfuls of sand straining them as the currents took the sand away onto the liverock as well.
I thought they were fun to watch, but they really messed up the corls world on my reef. Mine were huge though maybe smaller ones will do better for you.