bentonite is most notably derived from high silica volcanic glass/ash deposits. processed bentonite contains a high concentration of silica and typically sodium. processed bentonite comes in many forms (powders, gels, chips), most are pure bentonite and non toxic. However, some bentontie products are coated so it can be applied through water. the coating keeps the bentonite from swelling right away. the coatings can contain methanol, ethanol, and some other not so nice things but likely not in concentrations sufficient to kill yer fish.
