Have you ever heard of Lasix? I was told that if he is tied up and can't make his water, if I give him a shot of Lasix, he'll pass his water and be all right. Anybody else heard of this?
OMG, the amount of bad advice that gets circulated in the horse world is just unbelievable!
Lasix is a diuretic. It does not "fix" tying up which has nothing to do with "not being able to make water". Tying up causes a change in the color of urine because the body gets rid of the substances caused by the damage to muscle cells by passing them out through the urinary tract. And the common stance that looks like they are trying to urinate is simply an attempt to ease the discomfort of the muscle pain, not actually trying to urinate.
Lasix should not be given just willy nilly.
Also, tying up isn't due to a build up of lactic acid. That is an old idea that was disproven in studies.
There are multiple causes for tying up---electrolyte imbalances, genetic disorders that affect muscle cells such as EPSM (PSSM), defects in the way the body manages calcium in cells, heat exhaustion, overwork (just plain muscle fatigue), etc.
When you have repeat episodes, you need to set up the situation so that your vet can draw blood within 12 hours after an attack to confirm that what you are seeing is tying up. Then if that is the case, you and your vet need to look at what is causing it by doing some detective work and diagnostic testing.