I would avoid bleach-it's too harsh and kills healthy tissue, which in turn feeds thrush oranisms...plus, it burns.
I prefer to recommend apple cider vinegar and water 50/50 in spray bottle. It's non-toxic, it won't harm healthy tissue, and it corrects pH in the feet, and prevents thrush in the future if used about 1 or 2 times a week. For initial treatment, use it every day for a couple of weeks.
If it's not going away after that, you can try mixing Neosporin Plus with Lotrimin Athletes' Foot cream, 50/50 and use a syringe to deposit about 1 cc or mL in each crevice, esp. The center.
Or, if you wan to use a commercial prep, Clean Trax and White Lightening are the only ones I suggest. They work really well.
Do NOT use Koppertox, or Thrush Buster, etc. They are harsh, and kill irritate or kill healthy tissues. Idodine kills good germs on the hoof , which are necessary to keep bad germs in check.
Homeopathic remedies like tea tree oil are fine.
One thing to mention, nothing "hardens' the frog that is safe to use. Only proper stimulation by a heel first landing, contact with the ground and lots of exercise can do that. A good trim that allows the frog to contact the ground helps to prevent thrush and callous up the frog. Shod hooves have more trouble with that, as the mechanics of a shoe prevent it. Pads and bar shoes make thrush problems worse-constant pressure compromises circulation, the hoof needs give and take pressure, instead. (think massage vs. tourinquet)