I use ivermectin if I see redmite in the coop, as a spot on, like frontline for dogs.
To get rid of scaly leg, I get some vegetable oil in a jar and every night I dip their legs in it for a minute each leg, this suffocates the mite and makes the scales on the leg all soft and supple, which then the horrible lumps fall off, leaving the leg lovely and clean.
I don't often worm in their feed only if they start gapping, as I was told that regular worming upsets the insides, making them more likely to get ill.
I've had chickens for over 15 years and probably only worked about 1 a year and the oldest hen I've had was rusty and she lived for 9 years.