You have an outbreak of soil mites. Now I have done a wee bit o research on these guys and posted lots. So here's the deal I'll be brief but if you want more info just ask cause I have quite a bit o info on these things.
First, nearly 100% of soil mites don't eat roots they eat fungus bacteria, decomposing matter, etc. Only the bulb mite directly feeds on roots and they aren't known to go after weed.
Most of what you need to know is implicit in my statement, which means they like something in your pot. If you have chlorosis (yellowing of leaves) you may have a root issue like root rot (often caused by FGs). Further, mites are phoretic. They hitch rides on other animals or whatever. They will cling to the leg of an FG that may be spreading disease and the soil mite, which then feeds on the decay, bacteria, fungus, etc.
So mites in large numbers are an indicator that you have lots of bacteria, fungus or decaying matter. Also, don't try to eradicate them because that cannot be done until you get rid of the food supply. Mites also go into a suspended state of animation. So they'll be back when conditions are right.
Other interesting facts:
Mites are the only known animal to "devolve".
There are over 1200 species of just the Oribatid mite in N. America
One square foot a few inches deep of good forest soil may contain over 200 species
Mites are phoretic
