Killing Fungus Gnats?

don't provide a home for them, then you wont own a home for them attack all phases of their lifecycle at once, then get serious about IPM as a concept and doing soil indoors as a risk management problem (your health, pest, pathogens, your neighbors all of those)

In my opinion, you should only use that on ornamental plants. For plants that you still want to eat or smoke, I combat those pests with yellow sticky traps and nematodes, which works really well. You can also put a layer of sand or aquarium gravel on the soil, then fungus gnats can no longer lay their eggs.

Neudorff has an producht against fungus flies (Trauermücken) called "Spruzit Trauermücken­Frei". What you use is not recommended against fungus flies. Is it possible that your "Spruzit" is 14 years old? If yes, I would not use it at all. My choice would be yellow traps (Gelbtafeln) to have a feedback on how many flies are there (a good amount of them will be killed by it, but not all). And then nematodes or predator mites. They will not eat the flies, but their eggs.

Fungus gnats... you mean fungus flies... The best thing to do is to introduce beneficial insects against them... using plastic wrap will only make it worse as it creates a humid warm habitat for the... if you want to wrap it, please use mosquito netting or something similar...