Use just a VERY VERY VERY little neem oil.. Cold Pressed neem oil, that has been heated up a little, and mixed VERY well with a couple drops of dish soap...
If you use a small enough of an amount, you won't effect the taste of your buds and it will kill those damned little bugs that eat into your plants.
Hmmm, but what is the point of trying to fight any kind of insects, if I haven`t been able locate any on leaves. About gnats - could they be so small, that it`s impossible to see them with naked eye? Haven`t seen ay, neither in growbox, neither in room.
You probably had a bug that came and went. I had one with a leaf all chew up about three weeks ago. Since then, nothing. Some bugs will chew on mj but they'll quikly decide that they don't care much for the plant. If it was a bug that enjoys mj I'm sure there would be some sign of the critter.
Don't use poison on the plant(s). I wash the op with liquid raid mixed with some water in a bucket. Get the residual stuff meant for creepy crawlers. If you "think" you have to spray poison be sure to move the plant(s) somewhere safe away from the poison.
Put sticky tape around the plantpot(s) so the critters can't get to the plant(s).