UGF Substate

[TripleLexx]

Hi,
I'm using an under gravel filter system and am wondering if these are designed to work with soil substrate, like maybe a thin layer below gravel.
Would that be wise?

I don't really want to use the soil to maintain lots of flora, I only have a little java moss and I think I may just leave it at that.
The reason I wanted to use soil in my tanks is because I hear it helps with regulating your water parameters.

Thanks, I shall have something swimming in a tank soon I hope!