m0useanswered grow question 3 years ago Chances are they are fungus gnats, they love moist mediums and feed on fungus and baby roots when no more fungus is left.
Two of the best options are nematodes o BTi, both are living options. ones a parasitic microscopic worm and the other is a bacteria, they both will kill them.
BTi is sometimes in its own solution or in something called mosquito dunks.
nematodes come in many options I like the live ones more, a product called pot poppers. have had great success with this one.
Good Luck!