If he's not digesting his food properly that can be causing his digestive problems. Lady had repeated bouts of gastroenteritis, then three episodes of HGE. Adding digestive enzymes made a huge difference with her. I use Animal Essentials Plant Enzymes and Probiotics.
Lady also had trouble digesting rice. It came out the other end the same way it went in.
She does much better with oatmeal.
If you plan on keeping him on homecooked permanently, you will have to follow a recipe prepared by a nutritionist. Dogs have very specific nutritional needs. The calcium to phosphorus ratio is especially critical in dogs. If it isn't correct, they can have skeletal, neurological and cardiac problems.