Thanks for all the replies. I don't think that they are blood mites, these are white and look almost like fruit flies without wings. I'd get a picture, but I don't have a camera that can focus that well. I searched the whole tank and only found them in the damp substrate under his pile of feces and urine. He has a very clean white belly with no markings, and there was not a single dot on him, I even looked with a magnifying glass.

The strange thing is, I froze his mulch for two days then let it dry before putting it in his tank. The branches he has were soaked in bleach, then fresh water for days and allowed to dry. The only thing I didn't freeze was his sphagnum moss.

If the consensus is that they are harmless detritus eaters, then I guess that's fine and I won't expose him to chemicals...

the same thing happened with my planted goldfish tank. Suddenly saw all these little worms while planting new moss, freaked out and de-wormed the tank 4 times, convinced that the fish had roundworms, only to find out later that they are non-parasitic organisms that feed on bacteria and fungus in the soil.....