When I had my tank the main things, I had in there were shells, rocks and some aquatic plants as well. I found the way I had it all set up it looked really nice, wasn't overcrowded and the fish seemed happy with their surroundings which was what I was aiming for. I did think about adding a few more things but I really didn't want to overcrowd the tank and I also didn't want to place anything in the tank that the fish could potentially get stuck in.