Ok, but I heard that it was glass, dont know how true that is. I guess On the bag, it warns about bottom dwelling fish.I think that sand you linked would be better than PFS for kuhlii's, IMO. PFS (at least the stuff I used) was a larger grain size. I didn't notice any tearing of the fins but I did when I had regular gravel and eco. After moving them to playsand tanks their fins look great and they love sifting through the sand.