Is this normal?

[HornedFairy]

omg, sorry to hear about that infestation. Good to hear you cleaned the tank out and he's eating again now, that's great. I'm glad you put such a good picture up of the mites on his back, at least I know what to look for if mine ever has a problem. yea it's best to spot clean his tank on a regular basis, then do a complete clean out every couple of months, should help with any future problems.

[KingCam]

Many animals instinctually soak in the water when they become infested with mites (Yes, mites. That's what those were, I guarantee it!). They do this in order to drown the mites.

There are orange springtails, and those are good, but there are also orange mites, and those are BAD BAD BAD. Springtails will not swarm an animal like that, mites will.

Many new bags of substrate can be carrying mites, especially if they came from a pet store! Pet store bags of substrate are notorious for harboring mites. It is recommended to bake any substrate, store bought or not, before adding to a terrarium. (I almost never do this, and so far have been lucky enough not to get infested)

Keep a CLOSE eye on your frog, mites are incredibly hard to get rid of in some circumstances. Just when it seems like they're gone they will come back in full force. Mites can and will kill your animals if they get out of control.