I was in the same boat. Battling fungus gnats. I had tried everything, then
@TintEastwood recommended a cheap solution. I got this stuff off of AMZ, and it has some serious knock down power!.. I only use 12-13 drops per 50 gallons, and it killed all the larvae in the runoff tray with just one application. I still check every day, and see nothing but dead ones. I've never seen this kind of knock out this quick with anything else i've tried. AND, it's cheap, goes a hell of a long ways for the money. I can see the dead bodies in groups floating on top of the run off. I scoop up a sample, and check for life under the microscope... all dead. I used to use mosquito bits, neem oil drenches, etc., but always found live ones under the scope. Have not seen one live one since starting this application.
Edit: I still use large sticky traps on every plant to monitor adult activity, and it has dropped off dramatically. I haven't seen a flyer in days.
View attachment 5052208View attachment 5052209