If you have any standing water in your room, get rid of it. Those little bastards thrive in stagnant, wet areas. As for treating the water, I'm not a hydro guy but I know there are some organic products like "GnatOff" that work pretty well at killing the larvae. For the mature ones, I've used those plain old sticky fly traps before with pretty good results. Hang them between the plants if you have space. Just make sure a draft doesn't knock it into any leaves.