When choosing a substrate for a tank, you must also consider other living organism that you will put in it. But putting the fauna aside, I would suggest to choose nutrient-rich substrate or has a good CEC.

You can try using garden soil ( see Walstad Method ) or use a layer of Aquasoil, Laterite or Fluorite then cap it with finer substrate like sand or Aquasoil Powder-type. Capping it with finer substrate will help the DHG root and spread faster.

Further reading about Walstad method:

Walstad method