Predatory Nematodes. I use roots organic and it tends to have alot of fungus gnats. I saw ALOT of them towards my autoflowers transition into flower so I bought some nematodes. Make sure they are SF kind of nematodes. They have specific nematodes for specific pests but the SF usually takes care of most of the bad pests in an indoor organic grow. I bought the 50 pack of 1 million each. They are called pot poppers. You throw a pouch on top of your soil, water constantly for 3 days to water them into the soil ( they have no problem getting out of the little pouch and on into your soil). Suppose to work up to a 5 gallon pot for 1 pouch. I did one treatment 5 days ago and have been watering them in and I haven't seen a single fungas gnat in 3 days now. No pests at all.