His weight looks good to me, you don't want him tubby. My feed preferences would be timothy which is a good grass hay and adding Senior's and eliminating everything else you are stuffing him with. Senior's is for younger horses that have finished growing. It contains beet pulp, extra oils and probiotics. This diet will likely reduce your feed bill. I'd start him on two lbs of Senior's 2 x daily and likely leave it at that. It is safe to feed but no more than 5 lbs per feeding. An overweight horse can develop as many problems as a severely underweight horse.