I had a horse that use to get so excited prior to a race that he produced so much acid, that it built up in his muscles so much that he would loose control of his bladder and leak pee. My vet recommended electrolytes after (like you are using), but also tums 30 minutes before he would get excited.............. and it never happened after I used the combo.
The tums (just the one you buy at the store, although he really liked the flavors) help suck up the acid produced in the stomach and stop it from leaking into the muscles, and the electrolytes after help remove the remaining acid that had build up in the muscles (any that the tums did not catch).
Worked like a charm and he was much happier! Also because the tums are harmless I would also use it when we at home and I though he might get excited! It worked so well for him!
Oh and I used about 4 tums and he was 15.2hh but not a thick horse. I would not use more that 6-7, even on a large horse.