Okay so about 2 or so weeks ago I threw out and changed all my spadefoot toads' tank's soil.; due to little white soil mitey/larvae / fungasgnat thingies. (I KNOW EVERYONE ALWAYS CLAIMS that they are beneficial and harmless but I totally feel that my toads always end up seeming irritated and somewhat bothered by them - like itchy and awake more) ANYWAY it was straight coco soil (usually I mix with reptasand &or river bottom sand) So when I replaced & cleaned everything (replaced with coco/sand mix bottom layer of carbon). Not but maybe a few days layer I swear I'm starting to see something in the substrate again..but this time whatever they are they are DEFINITELY NOT the usual gnatty/soil mitey moving things. I don't know wtf they are but I am not tripping ,they are some kind of live organism,arthropodic mite things in there. Some of them seem to be a darker color maybe and a lot of it is like whitish kinda clustering "stuff" I dont KNOW it's hard to describe. It doesn't really seem like it's on the toads like stuck, but on their skin a little like when they first come up from underground.Idk . I think I should as soon as I can, take them out and "dry ice bomb" their tanks.
But first of two things
1) can someone please give me their opinion or possibilities of WTF these could be or effects /harm could be caused?

2) DETAILED INSTUCTIONS on dry icing the tanks? Like how much to use, how long, does it thoroughly penetrate all of the substrate, etc?

PLEASE SOME INSIGHT, THE SOONER THE BETTER, if I could afford New dirt I'd do that but can't. And want to stress toads out as LEAST as possible.
All response s will be utterly and gratefully appreciated.

THANKS.
IF FURTHER INFO IS NEEDED IN ORDER FOR ONES INPUT LMK .