This is interesting! I bought some prill beads ten years ago, from a "folk healer" who gave me some helpful advice re: Sea Salt and the adrenals...No one could say what the "prill beads" actually were, but I liked the water and it seemed to hydrate me better. I remember her saying they last "forever" (or many years was my interpretation).
Reading about zeolite on ebay, this source says their stones come from Bulgaria, and they look to be in chunk form (I guess the Prill gravel corresponds to "beads"...)
Anyway, this source says that they last about three months and then you should replace them???! Hunh?
Can you shed some more light on this prill/zeolite subject, please?