I went thru three gallons of Aloe Vera juice, from the health food store, and it wasn't worth the powder to blow it to the next county and back with gastric ulcers on my Arab who is a pasture ornament
If you're showing, you need something a lot stronger. My thought is to read up on Succeed. It's pricey but, there are some things in this life (and the horse's) that cheap doesn't get it
I have another horse with hind gut ulcers and probably also lipomas in the digestive tract. He's 25, also has Equine Metabolic Syndrome, hock/ankle arthritis and is now retired from trail riding.
Needless-to-say, he's under a lot of stress just from health issues
He is on Succeed and it seems to be helping. SUCCEED Digestive Conditioning Program Equine Supplement
The less grain products your horse eats, the better. I know that's tough when he's in training and showing a lot but, the less grain the better.
Rice bran has 22% fat and provides the horse with cool energy, instead of amping them up. It might be good to try your horse in rice bran and a high quality ration balancer that has all the vitamins/minerals.
Manna Pro makes "Maxi-Glo" rice bran in both meal and pellet form; I feed the pellets. It can be bought at Tractor Supply.
Ration Balancers are whatever high quality product is available in your area. I feed Triple Crown's 30%. My TC feed is made by Southern States, instead of Cargill.
If you feed your horse a lot of alfalfa, it might be best to reduce that and at least try a 50 - 50 mix of alfalfa and a good quality grass/mix hay.
A lot of alfalfa might be too much for his digestive tract.
What I am trying to say is figure out a way to feed him as bland a diet as you can, yet still get the performance you need. That can only be done with top quality brands and something to aid his digestive tract
Almost forgot, get a lot of water into him if he isn't a horse that likes to drink a lot. That's been a huge problem with my 25 yr old and the Arab ever since I've owned them (22 years and 19 years). Neither one of these horses want to drink a lot of water and irony of ironies, they both have some form of ulcers. They have water in their stalls every night and every night, the Arab's is un-touched and the TWH's is barely touched.
Hope this helps