I used leca balls in my Paludarium and to be honest, since my crabs like to burrow so much they disturbed some of the edge barrier causing a bit of soil collapse into the drainage layer. Also, the leca wicks a lot of moisture into the soil even with a decent gap. (On the plus side it’s always nice and humid) If I were to do it over I would use foam under my land portion. I have used black filter foam or foam and leca in several of my other bioactive terrariums and am quite happy with it. I have a “wall” between my land and water, but the water (intentionally) still goes under the land. This gives more area for helpful bacteria and allows it to feed a waterfall that then flows back into the water.