The thing that would bother me is what else is in there besides ther crushed limestone. Odds are its not checked for any metallic content nor otehr undesireables. I had a chance to get a heap of southdown stillin bags a fella bought that took care of commercial aquarium setups, that just happened to bit him in his backside when the southdown had a lot of undesireable compounds in it......IIRC its still setting outside his back door on a pallet.....Southdown was not founded solely to supply and for aquariums, it was a source of aggragate for making cement in the area, and therefore no down to earth specs were looked for as to its actual content and method of processing, as it met the requirements for its original intended purpose, making concrete. I have seen it first hand laying there in bags and there is spots in it that are reddish in color and also other formations of minerals growing.......Just not worth the risk, no matter how many folks have gotten away with it to chance in my tanks. Just my take on some of these proposed materials.
