yep id have to say king is spot on with the fungus gnat problem, go get a potato and cut a couple in half and remove the skin then place them on top of the soil, give it 12 to 24 hours then check the potato and if its fungus gnats you should see lots of white larvae on the potato as its an easy food source for them, i suffer with fungus gnats all the time but mainly during spring and summer,
the main problem is the soil been to moist so if your soil is to wet for to long then they thrive in these conditions so its best to let the soil dry out properly between waterings, also watering from the bottom also helps but you need to make sure the dish you have the pots sitting in is sort of sealed so the fungus gnats cant get into the trays or dish and get the soil that way, i cant get dunks where i am but ive got some sns products now that ill use when the gnats come back which i know they will do around march time.
they also can lay dormant in the soil during droughts so their a pain to get rid off, fly paper is a good option near the plants but make sure its the bright yellow type strips and not the sticky brown paper that you hang as this is no where near as good as the yellow stick traps, i actually made my own using double sided strong tape and got some flourescent yellow and orange card and covered it in double sided tape then stuck it on the walls in the grow room at the same height as the pots, this caught hundreds of them and finally get them under control, but after harvest i threw the soil out and started again as i just couldnt get rid of them, check any house plants as well. anywhere thats got soil and a food source such as plant roots is where you will find the gnats, breed like crazy. so glad i can hit them with sns now when they come back