What are you treating with? I treat it with banixx and it has always worked for me!
Well typical with rain rot you know it's gone when there are no more scabs forming and the hair starts to grow back. I usually continue treating for a few days after I notice no more scabs just to be safe. But some horses it takes a long time. I've been treating my gelding for about 2 months now and we are making some slow progress. He's healed about 76% of the way. But some horses are just more prone than others.