Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Sand as a substrate is not the best, but it can work.
Sand does not hold fertilizers the way better substrates do.
You will have to test each material to see what stays on top of what, but I have found a couple of general rules:
Fine stuff will sink through coarse materials (obvious example: sand will sink through gravel)
Heavy stuff will sink through light stuff (Sand will end up at the bottom if it is used to cap a lighter material)
If you decide to use sand, use pool filter sand. It behaves much better in an aquarium. Uniform particle sizes do not compact, this allows water to flow through bringing oxygen and water column ferts to the roots.
Use slow release root tablets.