...dishliquid, idealy Ivory or any biodegradable type. This give the medium (soil/less) an undesired taste to the larva the fungus nats lay. The fungus nat larva can potentially harm your roots, for this is what they feed on. The adult nat that you see flying is no harm to your plant, besides the eggs it lays in your medium. If you see these nats, this is a good clear sign that you may be overwatering your medium, and your maybe using too much petemoss in your medium.
...if you simply let your soil/less medium dryout until the leaves begin to wilt, you will kill about 80% of the larva the fungus nats lay. I'd try to time it to where you water one day before the leaves begin to wilt....this prevents the fungus nats for the most part w/ the dishliquid adding. Good luck.