What is the intended function of Power Sand in use with Aquasoil? It seems like many exclude it and still get good results. However I remember reading somewhere that it is meant to extend the substrate life. Certainly in my 10 gallon tank, the power sand + AS combo still grows plants well after 3 years. The only issue is that the white power sand granules get uplifted during rescaping and are visible amongst the dark AS afterward, but I would work around this in my new tank by containing the power sand within a grating to keep it separated from the AS. Since the tank is very large (4' x 2') I am of course interested in maximizing substrate lifespan.