Diet is definitely important to hoof health, but hooves chipping after a couple weeks could also be due to the way the hooves were trimmed. The farrier may be leaving them too long or may not be doing a bevel ("mustang roll"). It's also possible the trim is adequate at first, but the horse is not getting enough movement to maintain the bevel- in which case you might look into learning how to do that yourself and just give the hooves a touch up every couple of weeks or so.
When I switched farriers a couple years ago I saw a marked decrease in chipping in my horse's hind feet (the fronts were shod at the time). I'm not sure exactly what the new farrier did differently in his trim, but they went much longer without chipping.
“The horse is a mirror to your soul. Sometimes you might not like what you see. Sometimes you will.” - Buck Brannaman
"Nothing forced can ever be beautiful." - Xenophon