Unwanted visit

Fungus gnats are a sure sign of overwatering. Space out your waterings more, and make sure not to water until you have to push your finger down to between your first and second knuckle into the soil to feel moisture (doesn't really matter what finger, just don't use your thumb). Fungus gnats feed on the fungi that thrive in oversaturated grow media that never fully dry out. These fungi are fine deep in the soil by the roots of your plant, but not the top of the soil, where they attract gnats. Allowing the top inch or so of soil to dry out between waterings kills this fungus at the top layer, and the gnats will starve to death on their own. The gnats themselves don't do too much damage, but the overwatering sure can.