Fungus Gnat larve feed on moist root systems of plants. I too am doing autos like the OP and was plagued with the dreaded fungus gnats. I managed to kill all of them in 2 days by covering the pots with reflective foil tape. Like so:
This not only kills the gnats quickly and effectively, it also helps the soil retain moisture and the reflective material helps shine some light to the lower buds.