tiny tiny brown bugs in terrarium?

[flybyferns]

Sounds like mites to me.

I would wipe down the entire interior glass of the frog's enclosure with distilled water.
I would NOT us use anything else! Despite how safe it says...it is !!!!
You will ,likely, have to repeat this a few times.

Sometimes they ride in on the crickets/feeders and have not infested /or living in the soil.
Examine the feeder bin really carefully, including the exterior of the container and lid.

If they are in/on the feeder bin--- discard everything ( including the feeders) / rinse the bin in HOT tap water.

Wipe down the entire area where the feeder bin is stored ( including the horizontal surfaces)
w/ isopropyl rubbing alcohol / let it dry

I use this under my cricket bin and under my fruit fly cultures.
Josh's Frogs Bug Blade Mite Control Powder (5 oz) - Live Insects & Feeders | Josh's Frogs
-I sprinkle on the tray
-cover the powder w/ paper towel
-and place the bin or FF containers on the paper towel

( the bottom of the containers/bin are not physically touching the powder
-a little extra protection-so the powder doesn't end up somewhere you don't want it to be )

In my experience, mites tend to be more common in the winter then the summer. Dryer?