I'm not sure about mineralizing it, but I would think you could just submerge it in any container of dechlorinated water and wait for the ammonia to drop. Just test it until it drops and then use it. Actually that might even be beneficial to preventing a mini cycle from removing your old substrate. If it starts to cycle in the separate container because of the ammonia, and you don't let it dry out there should be some beneficial bacteria in the soil still when swapped. I would think that's your best bet, but it's purely theoretical because I've never tried to precycle substrate before.
Last edited by Loop; 03-21-2011 at 07:47 PM.