Hi. Getting rid of fungus gnats is not easy, but it’s doable. You have to break the cycle of eggs, larvae, babies, adults (about a week). You need to do it all at the same time, which means you treat the soil, the top of the soil, and the plants. Doing just one or two is useless. If you’re wondering where they came from, it is most likely from your soil.
Soil - nematodes (scyarid fly killer). They (microscopic worms) eat the eggs, larvae, and babies in the soil without damaging your roots
Top of soil - diatomaceous earth - it’s a harmless powder that kills anything moving on the surface. It literally shreds their bodies.
Leaves - bug spray. Your not in flower, so you’re lucky. Soak them.
Flyers - if you have flyers hang sticky tape.
The odds that you will get them all your first go is zero. There will be a huge difference after a week. After 2 or 3 you should be good.
I had this problem before. I use the nematodes now before I start. Good luck. It’s a pain in the ass. I’d suggest bud washing when you harvest to get the pesticide and detritus off.
Bud washing