Small White Bugs - Maybe from soil?

Well it seems that I'm now cursed with small white bugs that are getting into the cups with my seedlings. They're too small to take a picture of, but I'm assuming they are small white mites.

The thing is, they seem to be coming from my soil (Black Gold). The first time my seedlings got infected with them, I cloned them all and moved them to a new room - throwing out all the soil & containers with bugs.

Now I'm using a new room, but the new batch of seedlings somehow got the same white bug problem! While the clones, right next to them in rockwool, remain unaffected. Could it be there are mite eggs in my soil?

Anyone know what should I do to fix this problem? Is it possible the mites are coming from the soil, or is my whole house infected! Aieeee!

try using a barrier layer of sand on top of your soil.
and how often do you water ? lots of times bugs in soil come from over watering like fungus gnats.
because the soil is constantly wet the fungus in the soil grows well and the gnats larvae thrive.
try letting your soil dry out a bit and like i said use a layer of sand on top of your soil to block their reproduction. also maybe spray something with pyrethrin

I don't think it's from overwatering - They are seeds in small cups, and I would only be watering once a week, but it only took 1 day for the bugs to appear (only 1 has sprouted, but all cups are affected by bugs).