Fungus Gnats look like tiny black flies and will be buzzing around your plants. They will also lay their larvae in the soil, where they will burrow in and out your plants root zone. These larvae will eventually destroy the root zone which will stop the growth of your plant and lead to more severe issues. You will usually notice the flying gnats first and then the larvae soon after.
How to Cure:
Fungus Gnats are attracted to a wet environment as well as fungus on your soil. This is often caused from watering your plants too frequently, so be sure to wait a proper amount of time between feedings. This will help with curing the problem on its own. Next, you'll want to add some sticky traps in your grow room for the flying gnats. And finally, you will want to water your soil with a hydrogen peroxide mixture, as that will kill all of the larvae. You will want to mix 1 part hydrogen peroxide to 4 parts water, and you all want to water with this mixture each feeding until you can no longer see any larvae in the soil.
Gnat Sticky Traps
3% Hydrogen Peroxide
Dr. Earth All Natural Insect Killer