Why don't you buy a soil and do a "bottle test". Just put layer of soil in a glass jar and cover it with gravel and then add water. With a few tries, you should be able to add water without disturbing the soil layer.
You can then test the soil for cloudiness. You can also measure ammonia release or whatever.
I doubt that boiling will help prevent nutrient release, and it may hurt. Bacteria generate the "glue" (mucosal polysaccharides) that help bind soil particles together. When you kill them (by boiling), you temporarily destroy that process.
Also, you kill the nitrifying and other bacteria that come along with the soil. These bacteria generate the CO2 that will get your plants off to a good start. Don't kill them!
People who report trouble with soil often have not used it properly. It means that they don't understand submerged soils (which is complicated) and/or they didn't follow the directions. I've devoted a whole chapter to submerged soil chemistry in my book "Ecology of the Planted Aquarium".
My directions for using soils in aquariums are in the El Natural/"Low-Tech Substrate Advice" subfolder. Scroll down to my March 1, 2004 letter.
I still would do bottle test. It will give you a "feel" for working with soils that no amount of words can give you. Also, you're going to get some temporary cloudiness when you uproot plants in a tank with soil. That's a given.
Diana Walstad | 
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