I'm glad that the treatment has been working! Vetericyn is great –*not just for funguses, but also on injuries! I put it on some lacerations on Mudpie's legs and saw a huge amount of improvement! Keep at it, and if the problem persists, contact your veterinarian right away!
As for your electrolyte problem... sodium (salt) is an electrolyte. All living creatures need salt. We humans get enough of it from the regular foods that we eat, but horses do not. That's why they always need to have a salt or mineral lick available to them. The type of block/lick that you need depends on your horses regular diet. If your horse is fed a complete feed that's packed with minerals and gets a vitamin supplement, he or she probably only needs a plain white salt block. If your horse doesn't get that, he or she needs to have both a plain white salt block and a mineral salt block available (with constant access to fresh, clean water). One of the issues that I've run into is that the pressed salt blocks will melt in the rain, and some horses will bite off big pieces that they could choke on. I recently tried a himalayan salt lick, and I can say that I am NOT going back! Mudpie loves it, and I am confident that he's getting all of the electrolytes that he needs. He will stand there and lick it (it's like a toy to him, which is great because it's a healthy way for him to entertain himself) for hours! It apparently tastes great (because Mudpie is a really picky guy!) and it is packed with salt and electrolytes. You might want to give it a try! It's cheap and affordable and horses love it. I've also seen a "redmond rock" salt lick, which I believe is similar to the himalayan salt lick, but I can't vouch for it because I've never used it and I don't know anyone else who has.
To answer one of your questions: yes, feeding your horse too much gatorade can be unhealthy!
As for your horse problem... It was unclear to me exactly what the problem was, but it sounds like one horse recently developed behavioral problems and has been causing issues! Behavior like that leads me to believe that a horse is in pain. Seeing as he is a young horse, my first question would be whether or not he has had his teeth floated recently. Young horse's teeth are soft and easily develop hooks. A horse's teeth need to be floated once a year throughout its entire life, and this is especially important during its younger years –*often they actually need to be floated once every 6 months! There are a lot of things that could be causing this horse pain, so watch him or her. If he or she displays behavior like this during certain times, note your observations and let your vet know when you take him or her to be examined!
Another possibility is that this horse is learning how to settle in socially. Three years is about that time where the horse stops being "baby" and starts being "adult." He or she could just be trying to find where he or she stands in the herd! This is a time for testing the waters and learning whether he or she is alpha or bottom-of-the-totem-pole.
If the it really becomes a problem, talk to the manager of the barn and make sure that your horses are not in harm's way! There could be some arrangement that you could make to avoid getting your horse hurt.
The hills were bathed in moonlight, the shadows not so stark;
Silver light reflected off his brown hide as he held me in the dark
– I love you, Mudpie!