You are correct, Gnats around houseplants are usually Fungus Gnats and are a result of keeping the soil in your plants too wet. You could try drenching the soil of each of your plants with a chemical, but most recommendations simply say to allow your plants to dry out between watering. There are no aerosol products or spray products that will work because the gnats are a product of the larvae that live in the wet soil, and as long as the soil remains too wet, the larvae will continue to exist. You would think that if you could try and eliminate all of the adults that you'd gain control, but it only takes one female to lay eggs in the soil to keep the process going.

If the problem persists, then you could drench the soil in your pots with a pesticide like Neem Oil.
Thanks for your inquiry.

Happy Gardening!