I just had Sarcid flies/ fungus gnats they suck the problem isn't the flies its the larva that feed on the roots. I wound up with mine because i was keeping my soil to moist all the time. i think. Organicide at home depot is what Whiskytango recommended to me. used it and changed soil (when i re potted) that's how i got rid of them. But You need to look up pictures to see what kind of fly it was there are several others all of them are not really a good thing. if you don't see any more I wouldn't worry about it but take a close look at the fly and google "Cannabis pests" compare and it will tell you how to get rid of them.