You might look into a couple simple management changes that could solve that problem.
A change in farrier might do the trick. My trail horse has GREAT hooves, but I had a different farrier trim him a few times and all of a sudden his feet were chipping like crazy. Switched back to the old farrier and it cleared right up.
Also, my farrier (who has done wondrous things for my OTTB’s ultra-problematic hooves) has told me that when the hoof is crumbly at the bottom, it’s often times due to bacteria in the white line. He usually suggests keeping the hoof as dry, meaning no turn out in muddy pastures and making sure the stall stays dry. I’ve seen this do wonders for horses with “terrible” feet.
Otherwise, I would suggest SmartHoof or LinPro supplement-wise.