The Ultra is considered by many to be the finest domestic water filter of it's kind in the world today. Also called a hollow membrane filter this filter is the same size filter that is used in kidney dialysis. It is the finest (smallest micron) domestic filter available and will remove virtually everything except for the essential alkalizing minerals. Bacteria, Fungi and Viruses. The granular activated carbon medium in the both filters is of highest quality that comes from the UK and is NSF certified. Silver is also impregnated into the carbon to make sure that bacteria do not grow there. Because it is embedded, or impregnated, into the carbon so that silver does not leach into the water. Tests done show that no silver is released from these ionizer filters. Typically, if on city water we recommend the Biostone Plus however for certain well, problem water and where there is hyper-allergy issues we recommend the .01M Ultra filter.