Potatoes sound like just a breeding ground for more. Cover the top of the soil in DE, sand or perlite. Put up "gnat sticks"( Google) and sticky fly traps and they will begone before you know it. All the peroxide stuff Is useless IMO when its as simple as keeping top of soil dry with what I said, better with the de as the larvae will be shreaded. The sticky traps take care of the adults