I agree with Tom re: the greensand. It is an amazing media and was the standard way to treat iron 20 years ago. many companies still use it for many reasons. In certain areas, more modern medias are not as effective, it depends on the water, and local guys tend to have a great understanding of the unique water conditions in their area. Some companies sell it for financial reasons, the constant income of selling pot perm, and the potentially higher maintenance that goes along with it. Or just out of a companies inability to research, test, and experiment with newer technologies. Filox, Pyrolox, birm, Air injection, chlorinizaion/GAC, etc are just a few of the methods that can be used in place of greensand/pot perm. All of these technologies have their advantages and disadvantages, but in general, greensand usage has dropped by over 90% in the past 10 years with the company I work for. There are some very exciting new medias that should make their way to the market within 3 years that have the potential to replace many of the medias mentioned above. Like greensand, some companies will never move on to a new product. It can also be a "comfort zone" issue. Greensand works almost everytime it is used, but the handling of the oxidizing agent pot-perm should be avoided if at all possible.