One thing I do see is fungus gnats, but I haven't noticed any damage from them. Maybe they are impeding the growth of my plants? Could they be causing yellowing and necrosis of the lower leaves? Maybe if they are doing so much damage to the roots. But they usually don't damage established plants, only seedlings.
Far as I know the gnats are harmless to your plants and just are more of a pain in the @$$ than anything. Hand-to-hand combat is the way to take em out!