Here's a picture to show how I put the topsoil in the planter...
It is important to make sure it is covered on top and beneath with fine gravel. If it washes into the aquarium water you will get an algae bloom. Crypts grow a lot better if you give them some real topsoil.
That picture above show the Crypt. wendtii
'Mi Oya' that grew really big. For me the C. wendtii
'Tropica' (below) was more compact and had a more horizontal habit.