The Squid
Spaced-out CephaloMOD
Here ya go, dude. From my boi, Andy Botwin.
Fungus gnats are pretty easy to control, especially if you get them early. I recommend buying some mosquito dunks and putting them in something like a 5 gallon bucket. This is what they look like:
Let them sit at least overnight, preferably with some air bubbles mixing the water. Then use this water on your plants the next couple of times you water them. It will kill the larvae in the soil and your problems will be over. You can also add a fly strip to kill the adult ones that are flying around. I previously tried breaking up the dunks and putting pieces in 1 gallon jugs, but I've found it to be much more effective to just use a big bucket.
There are other solutions like putting DE powder or sand on top of the soil, but the fans can blow that stuff around & I really don't like a messy tent. I also try to avoid spraying things on my plants if I can, so the dunks are my preferred method.