What is "Mane 10"? and "a high quality" mixed half and half "so he doesn't get a lot of molasses"?
My apologies but if something has to be mixed 50-50 so the horse doesn't get "a lot of molasses", one of those feeds is not high quality. It's a sweet feed and that may be the problem.
My thought is a complete re-structuring of the diet so the horse has all the required vitamins/minerals without any molasses or grain. One of the best "hoof things" I ever did for all my horses was to put them on Omega-3 Horseshine.
I'm sure the biotin products work wonderfully and are beneficial in severe cases. With the exception of my club hoof horse, who is difficult to keep balanced, the only time my other three have chipped hooves is when they aren't trimmed correctly.
Two of those horses have metabolic issues, one did founder but they both still have strong, non-chipping, non-cracking hooves and the false sole stays put because they need all the help they can get. None of my horses eat grain or grain products and none of them eat anything where the protein source is soy
The hoof flexes, and the false hoof falls off naturally, but I remove it when it's already in the process of falling off.
I mix the grain based sweet feed with the pellet because he is a young horse in training, but too much sugar turns him into a monster. I'm a firm believer in grain based sweet feed, because horses in the wild eat a lot of naturally occurring grain. Plus the protein benefits of pellet, and the growing controversy of "sweet vs. pellet".
Mane 10 is a sweet feed. It's grain based, with almost no pellets, and very little molasses. With me adding pellets, and the quality pasture he get's, free choice of hay in his stall, daily exercises, I expect his condition to vastly improve. However, no hoof no horse. My gelding was very thin when I bought him (800lbs to 1100lbs), and running wild with 8 other horses. He's put a lot of weight on him, but these things take time. His hoofs were already in bad shape (no idea why, since he was wild, you'd think he would have a very nice natural hoof), possibly because of the all grass diet he had available.
Like I said, I'm a firm believer in grains. But my concern is, do I ad the biotin supplement once or twice a day? Horses naturally produce biotin, I presume him to be deficient from his lack of a nutritional diet, and any excess will be secreted in the urine, but the stuff is $14 for 2 lbs and I don't want to be just pissing it away (in literal terms)! Hahaha