Hello, you still want the sandy area like a river bank yeah? ADA has some decorative sands to choose from:
http://www.adana-usa.com/index.php?m...cPath=76_12_22
you know about the aquasoil types already it looks like. Yeah you can add a layer of power sand underneath the aquasoil for more nutrients and the added bacteria. actually you would probably be fine using straight aquasoil too.