Fungus gnats, fruit flies are not an injurious to plants or people. They are simply a nuisance pest that I have had to deal with over thirty years.

The best way to control these guys is three fold. If you miss one of these steps of you don't treat all of the plants, all bets are off.
First, regulate the watering, let the soil dry in between. Second apply a sticky board ( I use the one for mice cut into small sections ) Third one small nugget of mothball crystal on the soil top and on in the water catcher or well. Within two weeks the gnats will be gone. Don't forget to get rid of any standing water. They need the water to lay their eggs.

Thank you - I thought it was just me!
I also had used a brand new bag of Miracle Gro potting soil in recent months and within a two-week time period had dozens of irritating gnats flying around ALL my house plants! This is something I have never ever had to deal with before and I wondered if it could have possibly come from the soil mix itself... but that stuff was suppose to have been sterilized (or so I thought...).

Because I wasn't sure exactly just what the bugs were at the time, I tried using a Flying Insect spray on them and that didn't work, at all, and neither did soapy water on the leaves (my first defense against anything on a plant). I'm now going to try the "vinegar bowl" solution until I can get to the store to pick up some mothballs. Hopefully, something will work...I can't stand the flies anymore!