I had mites in a box of isopods I bought for a bioactive set up, luckily I noticed them before I put them in. I had to go through the dirt and pick out all the isopds and there were tons of baby isopods, took ages.
If I remember correctly the mites were more of a rounder shape and had little legs that were more to the front of the body. They looked a bit like the shape of a tick but VERY tiny where as the springtails are a longer shape. The sprintails move quickly, and will a lot of the time jump away if you poke at the earth near them but the mites will stay there. The mites move very slowly.
Springtails will crowd over frog poop, they love it, dirty little critters, LOL.
Hope this helps a bit.