What would you do? Fungus gnats

I have an infection of fungus gnats in my soil and it is stopping my seedlings from growing and slowly killing my current plant.

Is using hydrogen peroxide worth it or should I just get rid of all the soil and replace it all? Any suggestions

I had that problem once, i just got rid of all the soil because keeping infected soil around is just going to lead to more exposure

I always add ground up Bti(Mosquito Dunks) to my soil mixes now. When I first was getting started I got a serious case of fungus gnats and fought them all the way through harvest, I suspected they came from a the premixed soil(roots organic) I was using at the time. If you are already fighting the bastards as seedlings than you have a long road ahead of you but Bti can be used to control them, as with soil drenches of Azamax. I would probably just start over with different soil if it isnt going to be too costly.

I found using Fabric pots helps reduce Gnat infestation, Due to the top soil drying out quickly. Helps break the Gnats life cycle.