Re: Hermit crab tank with mites.
Do they hop around when you gently blow on them? Those would be spring tails. But they do sound like mites. There are many different types, if they are not latched onto your crabs then they are not harmful, they may be wood mites and are just feeding on detritus and the coconut fiber. You could change the substrate more often to reduce numbers a lot, do a whole sanitization, however I tend to not worry about them too much. They just show up when there is stuff to eat
Snakes, Lizards, Frogs, Salamanders, Newts, Tarantulas, Scorpions, etc.