Anyone ever considered using potting soil as a subtrate leading to health hazards? Thru evaporation or direct contact during water change or rescaping? Think legionaries or some other bacteria or fungus.
I've done many dirt tanks and they require a good amount if research and you do not want to rescape them. You want to cap them, plant and then leave them alone. You get used to swooshing above the substrate when vacuuming as to not disturb the cap. If you are a frequent rescaper or want to have brightly colored, delicate stem plants this method really doesn't work too well. When done right, however, you have a tank that has virtually no maintenance.
My 125 gal has a layer of potting soil mixed with a little sand, topped with regular black aquarium gravel. The plants don't seem to thrive, but the hardy ones do great. I've posted some photos in the gallery if you want to look. I've never had issues - even when I've had to replant or move things around. My pleco (he's a16 or so inches long) kicked up a huge cloud one time - made a massive mess on one end. Caused NO problems with the tank at all (which surprised me). Think clouds of dirt like when you go swimming and kick up the dirt. I didn't lose any stock - snails, shrimp, tetras, yoyos, kuhlis, etc - big community.
I have been using potting soil in my tank for many years and I have never considered there to be any health hazard with using it. Anything can be a health hazard, drinking too much water can kill you! But it is your tank, you need to set it up with how you feel most comfortable.
P.S. You don't even live in California where EVERYTHING has to have a toxicity health warning label on it so you are probably safe. Even their toxicity warning labels are required to have a toxicity warning label attached to them.