Any type of regular thrush killer can actually do more harm than good.
I HIGHLY HIGHLY HIGHLY recommend using a topical treatment for Mastitis (you can get it at Tractor Supplies). It's called Go-Dry. It's a suringe filled with white liquid. One suringe will be enough for all 4 feet...and there's' 12 in the package.
This is something you can apply every day if needed without fear of harming the frog or the hoof. It takes care of thrush quickly. Sonny had thrush extremely bad and it cured it up within 2 days.
Also to keep thrush away, try spraying a 50-50 solution of Apple Cider Vinigar (spelled wrong) and water. Use that every day and it actually changes the PH of the hoof so thrush cannot grow. But it won't harm the hoof.