Not sure what's recommened by Nebula. But, I like natural sprays that contain Rosemary, Peppermint, Clove. (EcoSmart, Bonida, Capt. Jack all carry something like this, I believe). It's very pungent and the gnats don't like it. I've seen them fall out of the air 5-6 inches away when I spray it. After each watering, I spritzonce or twice on the soil surface, and around the drain holes/saucer. That's enough to keep them knocked down.
Sticky fly paper hanging on the side wall can help. Also those sticky yellow cards. (You can buy a can of that sticky stuff called "Tanglefoot" and make your own cards, or rejuvenate purchased cards.). Lay the card on the soil surface.
If they're really bad, you can cut a piece of white poster board to lay on top of your container. Cut a slot from edge to center for the stalk. Make two so one covers the slot of the one below it. This isn't a perfect seal. But, makes it harder for the gnats. (If you're in a humid environment, this might cause mold on your soil surface.). One nice thing about these covers is that they reflect light up into the lower leaves. I think it helps.
Related to covering the soil, you can put the bottom of your container in panty hose. That keeps the gnats from accessing the drain holes.
To me, gnats aren't bad. It's a good sign that your soil is healthy. I just want to control their population. I don't care if I have a few. I just don't want them to be out of control. A little of all the above does that. (I've tried diatomaceous earth. I didn't think it did anything.).
