A few weeks ago I began experimenting with o/a trickle. The fist batch I tried seemed not to work on a couple of test hives. Mixed a new batch Saturday and treated ten hives. Went back this am and did a sugar shake test on one hives that had a mite count of 25+ and found two mites. I was impressed. The option was buying $200 worth of apistan to treat 45 hives. I followed Mike Gillmore's recipe (with one exception) which was as follows:

OA - 17.5 g.
Sugar - 300 g.
Water - 300 ml.

Mix your sugar and hot water to make a syrup.
Dissolve the OA crystals in a small amount of alcohol and blend with syrup.

I purchased oxalic acid at Ace hardware and a 60ml syringe at tractor supply.
My daughter had a chemistry scale. A digital scale that weighs grams could be purchased at walmart.
I weighted out the water, sugar and oa, placed 1/4 of the water in a widemouth mason jar. I then heated the water in a glass measuring cup in the microwave and dissolved the sugar in the hot water. I added the acid to the water in the mason jar and with the lid closed shook until completely dissolved. I then added the syrup to the jar and mixed thoroughly. This recipe made about a pint which was enough to treat ten hives.

Application: I filled the syringe and dripped five ml between frames with bees. The oxalic acid took care of the rest.

Notes:

1. I will need to do more mite counts to verify uniform results.

2. Not sure why first batch didn't work. I followed a recipe that used hfcs instead of sugar syrup. Maybe I didn't mix thoroughly enough.

3. It looks like this method will cost me about ten to fifteen cents per hive.

4. Hives are currently broodless