One of the essential ...

One of the essential problems you are having is plugging of the cartridge pores by the anthracite.  One of the easiest solutions is to add a precoat material to the incoming stream.  A material such as diatomaceous earth or other light-weight material will form bridges in the anthracite and maintain the porosity you need to increase your filter life.  

Alternatively, as was suggested, you could go to a prefilter such as a plate and frame or a sand filter. Either way you will have to backwash those filters, as you will with what I'm suggesting.