In case you haven't read it already, I'm including a link to a thread in the Container Gardening forum that should help to answer your questions. Specifically, here's what tapla has to say about reusing gritty mix and eliminating the bark component:

"Barring any incidence of disease, there is no reason you couldn't use the inorganic fractions of the gritty mix indefinitely. The problem, if you intend to use the gritty mix so it performs at its best, lies in how to separate all the fine particles of organic material from the inorganic material. From my own perspective, the effort isn't worth it."

"Screened Turface MVP mixed 1:1 with Gran-I-Grit in grower size or with #2 cherrystone will provide a well-aerated medium that will last indefinitely. Though you won't need to worry about removing the bark particles to reuse it, you will need to remove organic material shed from roots and old roots themselves, so it's going to present roughly the same picture as reusing the gritty mix."

One other thing to consider is weight -- gritty mix is very heavy, and bark is by far the lightest component.

Here is a link that might be useful: Re-using Gritty Mix

This post was edited by shazaam on Fri, Dec 28, 12 at 16:09