Having a real issue with fruit flies/ fungus gnats...

bti has been used on the world's food crops for ~100 years or more, so it's more than safe. Definitely don't need to spend 20/day on IPM to avoid gnats.. A 15usd quart of mosquito bits lasted 3 years... 50 plants, give or take. In my experience most products for these things are not very effective. Neem doesn't do shit. The holistic/natural stuff is usually trash, though this bacteria is definitely effective. It's even worse when you get into stuff that supposed fights WPM, lol. Lots of empty promises out there... lots of expensive products that are ineffective. It's the only preventative thing i do. Seen thrips once, but that was from a clone swap. Other people's gardens are dangerous, lol.

Larva is the problem... the adults don't damage anything. Though some yellow sticky traps will help get rid of them and fewer means less breeding, so that's a positive. Killing from both ends of the life cycle is a good idea. Kill the larva with Bacillus thuringiensis israelensis, or Bti. The brand name around here is Summit Mosquito Bits or Dunks. The brand name is irrelevant. The active ingredient is what matters. Dunks go in a reservoir, bits get top-dressed and watered in. It'll probably take 3 weeks to clear up. And the damage done to the roots will take even longer to recover, i'd assume. Hopefully these are photoperiods... get'em healthy again before flowering and they'll do fine. you may see ~1 gnat at a time for a while after, but it'll mostly stamp it out on its own. Relative to an indoor garden, gnats most often come from the store in the medium that you bought. Use BTI early on to avoid the potential problem... if you don't see any random gnat flying around after a month or so, you can cease use at that time. It's a great preventative measure that will kill off any nasty larva that come with the medium. Hands-down the most effective thing to do.

gonna be a rough time with living soil...solve the issue simultaneously for all stages of the pests lifecycle...which means you need to attack the adults you are seeing, the pupae you will see in a few days as adults, and most importantly the eggs/larvae. if the issue is 'bad' right now, then it has been really bad for quite some time...especially if you're thinking you have lost plants to it, then it has been a 11/10 alarm for a while now......mostly going to be relating to your watering habits, but your general OpSec as far as contact to room and soil health are not winning right now i think the best place to start is fundamentals with the gnats. educate yourself on the stages and your options. You will see that there is no 1-step for this. The complexity you will be scratching the surface on is why most folks cultivating for their dayjob have insane IPM procedures. I mean using twenty dollar bills left and right daily, just to be on top of it when it hits the fan

Fungus gnats are real, I use a product called neem attack, it's beneficial nematodes. They Fight and kill things that reproduce in the soil, specifically fungus gnats and thrips. A good application of Lost Coast is also pretty good Medicine . Yellow sticky papers also help and assist with assessment .There should always be pest preventative measures in place whether or not your showing signs and symptoms of an infestation. Moving forward, I would seriously consider rolling out some of the above mentioned pest mitigation strategies