I have killed thrips before and spider mites (spint in het nederlandse) with combos of diatomaceous earth (on the soil and around the base of the trunk) and spray for the leaves, as well as Hot shot pest strips. The hot strips kill everything, but the gnats have eggs in the soil and they fly out, lay eggs and then die, and more grow, fly out, lay eggs and die. So the strips do kill them, but they keep going, I guess they have a short germination. They are not long term critters and live in the top of your soil and munch on your roots. If you grow organically these are generally inevitable from what I have seen, and that is in different countries, and going back 20 years (gnats will be here until the end I fear), and also in hydro. Sprays for killing mites and thrips tend not to kill the gnats ability to just keep flying around from time to time. Other solutions include thick mango juice in a cup with washing up liquid, sit that in the grow tent. Yellow fly catchy strip things, the ones I always end up with stuck to my arm (grrrr). Sand in the top of the soil (this is a good one). Or go and by something like Gnat Off, you get special solutions that do kill the eggs and larvae. Ok, now I am itching and need to have a bong, lol. Nighty night to you all, peace, DST