Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Sure good soil is the basis for gardening on land or under water.
The soil chemistry is not too different.
The microorganisms are not all the same.
A good soil for garden or aquarium will hold fertilizers in a way that the plants can use them. Look for a material with high Cationic Exchange Capacity.
Sand does not have it.
Gardening in sand is not easy, aquarium gardening in sand is a bit easier, but not as easy as it could be if you had a better substrate.