mark wrote:

what do you think of using topsoil under the gravel in my planted tanks, do
you use it as well?

Some folks do. I tried it when I set up my first planted tank. It was a
disaster. If you ever need to move a plant or replant a plant, or if you have a
pleco or cichlid that likes to dig, your soil ends up as the top layer: on top
of your gravel, your water surface, your plant leaves, inside your filter,
everywhere.

I'm 18 months into planted aquaria, and I still move and replant plants weekly.
Soil ain't for me.