Treatment for white line/thrush, cancor, scratches, rainrot: Clorine dioxide at 20,000 ppm is activated using 1 deciliter chlorine dioxide, 1deciliter of vinegar with 4 liters of water. Or about 6 oz. per gallon; or as per manufacturers recommendation for use on livestock. Mix the 6 oz. of chlorine dioxide with 6 oz. of vinegar 5-10 minutes, turning it yellow, activating it to a higher strength.
I came across this recommendation in a magazine article written by a veterinarian a couple years ago and finally am getting around to testing it on a customer's horse that has a stubborn fetlock area skin condition. While this veterinarian seemed to have a lot of success with it, I'm still testing it. I purchased the chlorine dioxide on-line at Air solutions, phone # 515-577-9979, for $26.00/gal. Let me know how it works for you.
I've also found another very useful article here where they mention this supplier: Grand Circuit, www.grandcircuitinc.com. The sell it under the brand name, White Lightening.