What is wrong with my money tree?

I bought my money tree ( BTW, that picture is not my actual plant) at Ikea about 2 months ago. It’s been doing very well, showing new growth and bright green leaves.

Overnight, it seems like these small, gnat-like insects have invaded it. I discovered them this afternoon, crawling all over the aquarium gravel I have covering the dirt.

I’m not sure what type of insects they are, but they clearly have wings. I didn’t see any on the leaves, just at soil level.

I would like to know if anyone else has run across this, and what my options are to treat and kill the bugs without use of chemical pesticides.