I'm reminded of an Uncle who was into organic food. He was on his rant about how good it was for you as he opened a box of organic cereal. Mealy Bugs came flying out of the cereal box and we all started laughing. 'Well', we said, 'it's good for some things!' Sterile, well ground organic matter in soil should be fine. The problem is that soils made for gardening are not going to be of the same industry quality as those made for aquariums. I would not trust it. But if you are willing to give it a go, it will make a great experiment! I've seen a video on youtube where the guy used regular soil out of the ground that he baked in his oven to sterilize. It can be done, but you always run a risk of bacterial growth, fungal growth, and 'mealy bug' growth...hahaha.