I got a couple new tanks today, a 5.5g, a 2.5g, and a 55g, and I want to use dirt in at least the smaller ones. I have some soil that I have used in a tank before, but not as the substrate. I put in in some terra cotta pots with amazon swords before. It is MiracleGro Potting Soil. Is it okay to use as a substrate? I'm assuming it will be okay considering I had it in the terra cotta pots for about a month with no negative effects. If it makes any difference, it the soil has been sitting outside for a few months and has gotten rained on several times.