People cannot know things unless you have included them in your original post. It sounds like you have a great setup, but a horse with some sort of problem. You did ask for suggestions, and we all did our best. You could put him on Mare Magic, which works well (at least for the horses I have used it for), and it is not in the least expensive. If you cannot afford a supplement that might help, perhaps you really cannot afford this horse.
It is never the horse's fault