Walmart has very cheap potting/top soil that is very plain and nothing added to it, "EARTHGRO TOP SOIL". I've used it before in my aquariums and as people should know, any slightest particle of a chemical can kill off the fish in a tank. That's why you seal up aquariums and their filters when you need to paint any room in the house.
Seems like Home Depot also has it.
Seems like Home Depot also has it.