Pinhead size crawlies on Phal

[Newby phal grower]

There are pinhole-size black and brownish crawling pests on my phal. I re-potted but they are still there. I've been using potato slices for weeks, but they seem to be breeding faster than I can eliminate them. Is there an appropriate pesticide that can be used? I'd like to get rid of them - they nearly destroyed one of the others. Many thanks for help.