You might try painting the tank bottom to give the fish more security. The advantage of sand is that it provides a place for denitrifying bacteria to live. The disadvantage is that it's easy enough to vaccuum up sand, which isn't good for the sink at the other end of your python hose.
My grow out tanks are usually crammed full of hornwort, java moss, and water lettuce. I don't need the extra denitrifying bacteria substrate, because ammonia waste is taken up directly by the plants..