Agsorb Inc. seems to be the mineral source vendor for the majority of the these products here in the states.

I have APS from 2 different vendors (Schultz APS and Pond Care APS with Zeolite) and both contain archllite, which is a calcined montmorillonite and illite clay.

Anyways, evidently the sutibility of other "fuller's earth" products may vary regionally... notice that one region has a pH of 7-8