The best thing I've used is borax. Wash the foot with water and a hard brush. Pack it full with dry borax, then vet wrap and duct tape. Leave it on for about 24 hrs or until it falls off. I've left it longer. That will force the borax into the cleft, keep it there, and keep dirt out till it has a chance to work. Its very gentle on the tissues. It doesn't burn even when you get it into an open wound but it will kill bacteria and fungus.
Lots of good remedies out there, white lightening, thrushbuster, cleantrax.
I use Today, similar to Tomorrow, squirt it in to all the crevices, pack cotton on top, get a size 4 diaper and diaper up the horses foot then cover the diaper with duct tape, so much you make a duct tape boot almost. You may have to repeat this for a week or so, sometimes less sometimes more.
The nastiest case the old guy had I blasted his foot with water and scrubbed gently with dilute Betadine, then rinsed and went ahead. His heels pretty much sloughed off but they look good now.
I get Gorilla tape and Today at the TSC and the cotton balls and diapers at the Kroger grocery store. It's worked for me and I can just walk in and buy the stuff. Easy peasy. Except watch out for the Gorilla tape, it has a will of its own and is very sticky.
White Lightning! I used it for the first time, soaked the test hoof twice, and the central sulcus thrush was GONE! I will definitely be using it any time there is anything funky going on, and will be soaking the other 3 hooves today.
Also, I like to put soap (I have Ajax, that's just what was in the pantry) and water in a squirt bottle, and spray, scrub with brush, spray again. Soak cotton balls in liquid thrush treatment of choice (currently using Life Data Labs Hoof Disinfectant) and pack crack with cotton balls. Do this as much as you can, so every day/every few days.
Use White Lightning at least 2x a week in the beginning, then taper down as thrush goes away.
Pick hooves at least twice a day, and check to make sure there is no imbalanced vitamin/minerals in the diet. Too little Copper, Zinc, Amino Acids, too much Iron, ect.
"On the back of a horse I felt whole, complete, connected to that vital place in the center of me...and the chaos within me found balance."