Scaly Leg Mites are killed by suffocation, I believe.
This is what works for me every single time, usually with only one application:
Scarlet Red Oil
It's for horses and comes as a spray or with a daubing device. Get the latter. Remove any dirt first, but the crusty bits should be left alone. Sometimes pulling them off causes the skin to come away as well. If you've washed the foot, pat it dry so as to not dilute the oil. Daub it on all over the foot and leg. Put the bird on wire for a couple of hours to let it dry.
I've had birds with legs so affected they couldn't walk. This doesn't work overnight, but it works. Eventually all the mite dies and slowly, the crusty bits begin to fall off on their own accord.
I've had to do a second application only twice because the oil wasn't able to cover the entire problem.
WARNING: Do not use on birds you want to show. The legs are stained pink for about a year, sometimes more.
Oh, and a word on Adams... They've changed their formulation since the days they were the acknowledged superman of pesticides. Whatever the wonder ingredient was, it's gone now. If you read the label, and then the label of several other spray-on Flea Controllers, you will find it's identical. I called the company to verify this.