I was wondering what substrate you would reccomend for a 10 gallon shrimp tank I am going to set up. I saw that you can put a layer of potting soil under the substrate in the December 2009 Freshwater and Marine Aquarium magazine and I was wondering if this works good? Has anyone tried it? I don't want to pay a whole lot for substrate so I thought the dirt under gravel method would be an inexpensive way to go.