I've done it but remember that many potting soils contain lots of light weight
organic particals that will float. When I do it I always use mushroom compost
or something similar. This type of compost is heavy and will stay under the
sand. it's also a good idea to put a barier of egg crate lighting panel over
the compost to prevent fish from digging it up.

Moon
remove nospam from e-mail to send to me, I grow trees in aquariums like bonsai.
I breed dwarf crayfish, great for planted community tanks. If you can get me a
shovelnose sturgeon fingerling (Scaphirhynchus platorynchus) no wild caught
please, contact me