potting soil

I am setting up a heavily planted 40 gallon aquarium. I want to use potting soil capped with playsand for the substrate. Are there any negative effects to using potting soil in an aquarium?

I just started a planted tank and was wondering if potting soil is bad. I already put it under my tank :-?. So my tank has potting soil with no fertilizer and a layer of sand over it. The thing is when I added the water some of the potting soil came out and settled on top. My filter cleared the...