To get rid of gnats in the house a few different strategies are recommended ... hydrogen peroxide or bleach in the drain. This should kill them instantly, but repeat as needed.
There really is no need to spray the leaves since the adult gnats are not feeding on the leaves. Doktor Doom House and Garden is a product I have used and found very effective. Spray the ...
Though not quite as effective as Bt, these natural insecticides can kill fungus gnat larvae when watered into the soil. Spraying the foliage is not effective for fungus gnats. Use natural predators.