Anything over 200F for an hour with a small amount should do it. It's best to store it in a well-sealed bag with the air pushed out after that to stop it from reacting with moisture in the air. Never add powdered supplements of any sort directly to a tank - too much risk of local pH swings in this case and more generally too much risk of the substance being caustic on sensitive animal tissues (fish gills, snails, etc.) if they make contact before fully dissolved.