THE BEST is soaking with White Lightening. It should take just 1-3 soaks to get rid of the thrush. To prevent thrush, I really like the dry/powder treatment No Thrush. White Lightning | Grand Circuit Products http://www.nothrushshop.com
I have tried almost every thrush remedy on the market, and lots of home-made recipes too. The area of Arkansas I live in gets very boggy when it rains and my horses have thrush nearly year-round if I don't stay on top of it. The above two treatments are the only ones that seem to really work effectively for me.
Diet is also a factor. If your horse is lacking in zinc and/or copper, your horse is less likely to fight off issues on their own. PH levels and high starch diets can also be a contributing factor. Shoes hold in more "junk," so barefoot horses (IME) tend to be less thrush prone.