Ian, I have a little bit different formula. This is for 3-5 hives.
Cure is given when when brood is away and bees are in winter ball. +5 - +10C (41-50F) is good temperature. Bees may fly back to hive at this temperature but even colder is good.
Brood area contains mites. It it best to destroy them if it is small. If bees do not fly and you put frame out, birds will pick brood from frame. If you leave brood you may have hundreds of mites there.
Get a vaccination syringe from drugstore so you see ecaxtly needed measure to spray.
You may put paper on bottom boad before handling. You will se how much you get mites when you take it away.
Take 7,5 gr oxalic acetic powder and put it into 0,1 liter warm water.
Take 100 gr sugar and dilute it in the solution.
(Euro coin is just 7,5 g. You can weight your coin and you can use as weight. Own balance is easy to do. Our coin weights are in internet. There are cheap digital kitchen balances in stores which have 1 g accuracy. )
This 160 ml volume is enough for 3-5 hives, depending of the amount of bees .
Give droplets together 4 ml solution in one gap of frames, which is full of bees from edge to edge. Not more.
Do not give for one box hive more than 40 ml, and this only for hive which is totally full of bees.
Do not give for 2 box hive more than 50 ml.
DON'T GIVE TWICE HANDLING. It is harmfull.