I'm having problems with the substrate fly. I...

Bti - Bacillus thuringiensis (israelensis) - Kills larva of more than just fungus gnats. Can be used pre-emptively. Pyrethrines - kill on contact sticky traps.. obvious.

Sticky traps and better dry-wet watering cycles are your best tools now. Fungus gnats thrive in constantly moist topsoil – let the top 2–3 cm dry out completely between waterings. You can also top-dress with sharp sand or more diatomaceous earth to block them physically. For real long-term control, release beneficial nematodes like Steinernema feltiae – they hunt and kill the larvae directly in the soil and are completely safe for your plants. If it’s still heavy, a BTi treatment (like mosquito bits) can also help finish them off.

Let top get get dry Add rocks or mulch to top soil Yellow sticky traps If you can’t get rid clean grow room after harvest and throw away all soil and clean pot then let room sit for 2 weeks b4 buying new soil

Letting the top of the soil dry out. You can also scoop out the top inch or so of the soil and discard it and then add new clean soil/medium that isnt infected by larvae of fungus