for fungus gnats actually the solution is very simple : they need moisture to keep their eggs safe, so as long as you stop overwatering then they will just basically disappear within a few days. You can see the symptoms of overwatering like the puffy space between the veins of the leafs and the downward curling tips . the main thing is to respect a very strict wet dry cycle, just leave it one more day than you usually would or even more if necessary. diatomaceous earth works well, but my favorite remedy for any type insect is actually biological : use bacilus thuriengiensis , this bacteria doesnt harm the plants at all but it will parasite the eggs, larvae and even go into the brains of the flying insects... after you add it you'll start seeing the flying ones behave in wierd ways when they fly and in like 10 days everything will be gone. Hope this helps ! 🚀