Ask two horse people, get three opinions, right? Everyone's got their favorite stuff for use around the barn. I'm especially picky and I'll often burn through several possibilities to get just the right thing for my problem. With that in mind, I'm going to do occasional product reviews of things that I've used and loved for years. None of these are endorsed unless I mention it up front.
I've talked a little bit about our recent struggles with white line disease in both of Tristan's back feet. I've been paying too much close attention to his front and it wasn't until he started chipping excessively in the back that I took a neurotically close look at his hind feet and bam - clear indications of white line problems.
I was first introduced to White Lightning by a barefoot trimmer that I loved, who worked on Tristan for about a year and was a friend of my first trimmer in Vermont. She recommended it for a touch of thrush that he had going on at the time. Since then, I've always kept a bottle on hand. I tend to think of it as big guns: it can be a pain to apply and use, but whoo boy does it live up to its labeling.
The gist is that White Lightning is a chemical that reacts with vinegar to produce chlorine dioxide. For small, short applications such as the mild thrush that first led me to the product, you can mix equal parts White Lighning and vinegar in a spray bottle and then thoroughly spray the bottom of the hoof. It needs to be mixed new each time, as the chemical reaction is what counts. You don't need much at all if you're using this method - just 2-3 tablespoons of each liquid.
It is a pain but thankfully Tris is great about soaking after our abscess extravaganza. Drop a flake of hay, untie him from the crossties, and he. will. not. move. For horses that get more antsy, duct tape is your friend. Cover the bag, and get it nice and tight around their pasterns, too. (For the horse that truly won't tolerate soaking, this stuff probably won't work for you, alas.)
It really works. It knocks stuff out cold. For really persistent problems my strategy is to soak at 1 week intervals but I promise you will notice a difference, especially if you keep things at an even keel in the interim - stay on top of picking the feet out, etc.
Caveat: many people find that their horse's hair can be bleached by the gas that the mixture produces. I've never run into this problem but I'm sure it's possible.