With one magazine showing a photograph of some one holding a sample of the crushed rock in cupped hands. This product does an excellent job at what it is recommended for. But as yet no one has pointed out the hazard of using this material.
All of the chemicals we use to treat our Koi are potentially hazardous. We are constantly reminded to use gloves and masks when handling them.
Zeolite is a silicate mineral similar to asbestos. Of the 3000 and rising numbers of people every year diagnosed with Malignant Mesothelioma (an incurable terminal disease of the chest lining caused by breathing in silicate dust) a small percentage of cases have been linked to Zeolite .
Asbestos has been used for years in many products in our homes, schools, and cars. So it has been difficult for a great deal of the population  to totally avoid it. The number of people coming into contact with Zeolite has to be extremely small indeed and yet it shows up on the statistics. The implication is that it may be more carcinogenic.
There is a web site www.intelihealth.com that gives a full explanation of the disease, the causes and the risks. just click on the link below, I hope this will assist in people being able to make an informed decision about this product.

http://www.intelihealth.com/IH/ihtIH?t=24655&p=~br,IHW|~st,9105|~r,WSIHW000|~b,*|

Roy French