Many on the East Coast are having terrible thrush problems because of the very wet year. My paddock has been wet all year, and the horses are suffering.
I have treated with several things this year.
Understanding what thrush is, and is not, will help. It is a bacterial infection, but can also have fungi feeding off of what the bacterial infection kills. Try searching www.TheHorse.com
for more info on the cause.
DO WASH YOUR HANDS and nails after cleaning the hoof. You will have a zoo of microbes on your hands after cleaning. You don't need to go overboard. Simple soap and hot water will clean your hands. Yes, I wash twice.
There are many commercial products out there. Iodine will kill the infection, but also stains your hands and shoes. It will also dry the frog out. Another poster suggested TODAY. I use the the cousin to this, Go-Dry. Both are mastitis anti-biotics. They come in a tube that is useful for getting into the crack that forms between the heel bulbs. Go-Dry is cheaper. Some farriers will mix a triple anti-biotic cream (human generic) and Lotramin 50/50, and put it in the empty Go-Dry tubes. It is rather thick, and harder to press out, but it works. After trying to mix this, I went back to the purchased.
There are several products like CopperTox that are copper-based. They do work, but can harm the coronet band if they drip onto the hairline. ThrushBuster is iodine based (I think). White Lightning is preferred by some. It is more complicated to use, but works well.
Here's the bottom line. Treat it every day, and don't stop until the frog has grown out. Air and dryness will help. It's a pain, but the horse will be healthier for it. You are not alone, and aren't the first horse owner to not notice the thrush right away. Just keep treating until it's gone.
I'll make one more suggestion that I am playing with now...I use Eqyss Micro-tek shampoo full strength on the entire hoof, let it sit for at least five minutes, and rinse very well. Then use the Micro-tek spray every day. It helps to heal as well as kill. The active ingredient is an antimicrobial that is safe for humans and skin.