Add gravel! Not the colorful kind, unless u like it, in my opinion you should get gravel,
View attachment 235221, that would be nice, as far as decoration you should have a nice big/small centerpiece with decorations such as fake/real plants in the background and the sides, the rocks are nice too, some from petsmart or so, it looks like u have an air pump? Add a decoration that includes one, that would be nice as well, mine is a hut with a spinning wheel on the side and makes the air go up to the side so it looks like bubbles are coming from the chimney, that's all I have to say! Good luck! Keep us updated