A 1500 Watt hairdryer aimed at adults will kill them.While not fesable for large areas,it can be effective in small growing spaces and head off an infestation.
Bacterial solutions,predator nematodes,nocturnal soils mites and a parasidic wasp.All of these are benign to human AND pets.
Rove Beetle;Soil dwelling insect that does quite well for fungus gnats if pray is abundant.Produces fast and well.Assuming the pray is there.
Hunbter Fly or Tiger Fly:
Controls maggots and adults.
Nematodes:
Predatory mite:
Parasidic Wasp:
Pesticides and fungicides:
Cimmamon oil and Tea:
Cinnamon oil serves as a repellant for multiple persts including fungus gnats.Also works well in combination with other herbal or planyt oils that function as repellants,Including corianderoil,Neem oil, sesame oil,and blend oils or horticultural oils such as ed rosenthals zero tolerance.
Peppermint tea:
Peppermint tea(STRONG) kills fungus gnats as well as larve too.
Pyrethrum:
Sprays kill adults and can be used as a drench to kill larve in the soil.
the easiest way:
Use Vectobac Gnatrol,and Bactimos.All contain Bacillus thuringiensis var. israelensis.This strain of BT controls the maggots,unfortunatley its only avaliable in gallon jugs.Most garden centers wont have it yet check your local Hydroponic stores..Neen oils and insecticidal soaps as a soil drench.