Have you seen the vet for a fecal exam to rule out parasites, giardia and coccidia? If not, this should be step one. I would also change his diet to something even more bland. Boiled chicken and white rice (no bones, no skin) works well. This should help to firm up his stools. When the stools are normal again, you can start to add in his regular meals little by little.
Let me know if you still have questions.
