They probably are not harmful at all. See:

http://www.redwormcomposting.com/worm-composting/a-mite-is-a-mite-is-a-mite-not-quite/

If you still want to reduce their numbers (you will never get *RID* of them), there are many ways.
Some people use melon rinds, once the mites cover the rind, just rinse the mites off it down the sink, then put the rind back in.
Another way is to use an old tuna fish can. Put something 'meat-like' in it. A small chunk of tuna for example. Then bury the can so the top is even with the top of the bedding. When the mites swarm it, either rinse them down the sink or put the can in a baggie and stick it in a freezer.
You can also use a micro torch to kill them. Just wait until they swarm the bait, then flame broil them.
I've done all this stuff in the past and came to the conclusion, that the mites don't hurt anything and it's just a waste of time to mess with them.

The numbers will die down also as the worm population goes. With the good aeration of the Inn and lots of surface area it does seem to grow large populations of other creatures. I started with tons of white mites, moved to red ones, then that population died down.

Happens as in new bins the food tends to sit around more giving more food to mites. Once the worm pop grows, that gets reduced and the mite population drops.

So as long as the worms are happy and breeding, all is good.