an affordable 100% solution to this problem is to use Safer brand caterpillar killer on your medium, that is if you're more than three weeks from harvest. Those could also be fungus gnats, in which case it isnt the adults you need to be worried about. Get the Safer shit either way, it's a great, great product that has been used by serious gardeners outside the weed scene for a long time. I bought a bottle of it for like 11 bucks a couple years ago, and i still havent even come close to using it up.
People are so misinformed about those yellow strips. You see how the have squares on them? Yeah they do kill bugs, but not effectively. Those strips are really a tool to get a census of the bugs. You hang one up for 24-48 hours and count the bugs in a square. While using some other effective treatment, you can count and estimate the bugs population by counting the dead ones again, or using a new strip or card. That's how I use them anyway, and they work great for that! i wouldnt count on them to knock out a fungus gnat population.
Those fungus gnat larvas actually do a lot of damage. They slow plant growth down to a standstill if they get bad enough, and I've seen infested root zones on a friends girls that looked heavily darkened and...well just shitty.Nuke the little bastards man, they're easy to get rid of when compared to mites or something, get the Safer brand shit!
Finally anytime you are treating something in the root zone it is especially important to use an enzyme mix like Hygrozyme, or Sensizyme. I'd say always use them nomatter what anyway, but they really help scrub up the damaged tissue left in the roots from larvas chewing on them. I'm making this a somewhat long post, but that's cuz i want you to get rid of them fast. Again it's not like mites, this is something you can nip right in the ...well..BUD so to speak! Good luck dude! Bomb 'em with something potent!! (and non-systemic, lol)