I have gravel, currently i have a moss ball thing and my tank is still cycling....I messed up and did not do any research and i was unaware of what cycling was.....i went out and bought 2 neon tetras, 2 cory cats, 3 cardnial tetras and 3 others whose names i do not know, i know this is over stocked but i have been doing the water changes and taking good care of the fish...