fungus gnat killer??

A combination of Sticky Traps and Watering with BTI worked for me.

biological neem oil with emulsifier, 1ml for 1l and you're gucci, you could drink it or put in on your skin without a problem and will ONLY kill insects

I've used this successfully with thrips, I used BTI on gnats in the past with decent results. Combined with sticky traps, and letting soil dry right out. It was when using Gaia green, worm castings mixed with promix hp and additional perlite. The soil took waaay too long to dry out and caused lots of issues, the gnats being one of them.

Nematodes. Just buy the appropriate sort and they will be gone in a week.

BTi or Nematodes, I like Nematodes as it works for me. used BT before as well just like nematodes more. Bother are safe and effective. DE is good in soil for Si, on top it can kill bugs if its dry, but its more a respiratory irritant for humans. not worth it IMO. Long term exposure is asking for COPD. always wear a mask when handling it and wet it down much like perlite dust and such.

Bti. Use it pre-emptively because gnats come with soil/substrates due to how they are stored and shipped. If you use it the most you'll see is an occasional gnat and most times not even that. it's a bacterica that's been used on the food you eat for decades, so it is safe and you are potentially exposed to it nearly everyday already. in america it comes as "mosquito bits" and "mosquito dunks" and should be effective with just about anything that have a larva life stage in your soil. Adults don't cause any damage but annoyance. The larva is what damages the plants. With an ongoing issue, kiling them at multiple points in their life cycle only makes them go away faster. DE is a mess, but can be helpful as long as it stays drie, so putting it on the soil is mostly worthless... will add some silica from what i understand but if put down in any visible layer it'll also potentially dam up the water at the top and reduce absorption rate significantly. Put it on the ground around garden or pots, but don't put it in your pot unless well mixed into substrate (for silica, not to kill pests, because when wet it doesn't do much for pests)

Accept them and live with it.As long as they're not out of control they're not a problem.They say you should expect them especially if using organics.The best thing I found was predator mites.They w ere around £15,I think it was ebay of all places.I always have loads of hanging strips which catch loads and the sticky cards near the pot.The sicky traps and making sure the surface of my soil,coco is drying out completely keeps on top of them.In my room I'll have anywhere from 2000-300,10 pots.150 ltrs medium. I guess.I wouldn't used any cemicals of anything you're consuming but that's me,I eat organic.

Diatomaceous earth was what I used when running into them. I swaped to a peat based promix hp and havnt had to fight them like other media. Hope it helps some.