my rundown on fungus gnats.. ymmv..
they repopulate via the sewers here, as is likely in any urban or suburban area.
i tried keeping the top of my medium dry and using BTI (mosquito dunks) for watering, which reduces them, but not to an extent where they won't still chew down seedlings and stunt root growth.
the winner for me was agsil 16h from customhydronutrients.. this lacerates the larvae in the soil. not a fungus gnat to be seen most days. this needs a ph down to balance it, and between the two, likely since this is new for me, my plants are still not optimal, but there are no fucking bugs.
i grow seedlings in a netted box with true cypress cinnamon sprinkled on the bottom.. this does repel them. don't get it in the soil, it retards roots.
i had little luck with vinegar traps. i am also starting to use an inch of perlite on top of my media (others recommend sand) to reduce the amount of potassium silicate i use.
