Anabel, I'm not saying those things because I disagree with her. I'm saying them because I'm NOT feeding him grain for fun, and I'm not feeding it to experiment. She called me a child and said I'm going to hurt my horse, and said that I'm experimenting with him in a dangerous way, and I'm not!
I wanted to experiment with ONE kind of grain. And, I'm not treating him like a lab rat AT ALL. Since when was it not safe to switch grains and see if your horse did better, worse, or no change at all? Last time I checked, people do that all the time. It can be dangerous, but as long as you try things slowly and with patience it's perfectly safe.
Ok... You also never stated the horse was underweight. In the OP you said he is a "fairly easy keeper" and you ride him 2-4 times a month.
As has also been stated, if if ain't broke don't fix it. 99% of horses in your horse's situation do not need grain, and feeding it to them will lead to obesity and related issues. If he is underweight, upping the hay is going to be a way healthier way to address that than adding stratchy grains to his diet. If more hay is not available, then the addition of a ration balancer would be OK.