I have about 15 house plants besides my grow, and long ago began my battle with fungus gnats after someone gifted us a plant which must’ve had them. I had never had an issue prior, once this plant came in, it was insane; they spread to every other plant in the house and got so bad you could see them in the air.
I’ve used a 5-part attack against them and as of today, I’d say I’m about 95% of the way to full eradication. It takes fighting them steadily for a while to make sure they don’t have a window to build back up. One adult can lay 200-300 eggs, so it’s a big battle.
Part 1: Set up some of those yellow sticky fly paper traps around your plants and near windows.
Part 2: I also used a mechanical catcher from Amazon called “Katchy” which uses ultraviolet light at night and a fan to suck them in. It’s very effective:
Part 3: Neem Oil both sprayed onto the plant and onto the soil before AND after watering; before so watering pulls some into the soil, after to help keep a barrier on the soil surface where eggs are laid.
Part 4: Top-dress the soil with Mosquito Bits, watering draws this down into the soil which kills the larvae.
Part 5: Let the top 2-3" of soil totally dry out between waterings. The eggs and larvae need water and moisture to develop and survive.
Following this over time they’ve become less and less and I only see a random one or two in the house here and there now. I’m keeping the assault up until there are none left! As far as my grow tent being set up new in a house with an existing fungus gnat problem, it’s been a very minimal issue. I have seen a handful of them in the tent, but as I’ve gotten it under control in the house and only using neem oil on the plants in the tent, it’s been a couple weeks now without a single gnat in sight inside the tent.