I am moving in a few weeks and I have started a planted tank, nothing serious but i would like to continue to add more plants and see more growth. I have sand in my tank and was thinking that since I have to break down the tank for moving anyways I would love to add soil under the sand. I just don't know what to add. I had ready about some really expensive types, but have also heard about using plane old potting soil? Does that mean I can go to the Depot and just get a bag of potting soil?