I haven't seen their tanks in person, but if there is a space in the front you will want to fill it with some thing. You can use Hydroton, Lyca, Rocks... really anything that wont break down. Seperate whatever you put down there form the soil above. I prefer to use Fiber glass window screen for this. It is cheap and you get a lot of it You soil you will want to make at least 3" deep.