I kept marbled gobys for almost 20 years now these fish will grow fast and very large if properly cared for. i have a breeding pair with a 16 inch male and a 9-10 inch female. also have a few young growouts one has made it 8 1/2 inches from less than 2 inches in about six months gravel doesent matter but these fish thrive in tanks with lots of wood rockwork and caves. they will eat anything that will fit in there mouths and defend there caves against any fish. also have spotted sleeper gobys jade sleeper gobys and purple spot gudgeons all from the eleotridae or sleeper family. i have lost lots of fish to my gobys pm me a number and i can send you video of my pair. lost a jeff rapps dorado and a shortnose gar to my female spotted sleeper and i was pissed but thats the risk you run with these fish. i feed large goldfish and rosey reds that i feed heavily for a week or so cichlid fry that i raise from my pairs, crayfish ,earthworms, tilapia fillets live and frozen shrimp and small crabs. hope this helps steve