Go got some Mosquito Dunks, which is the Bti, sold at most home improvement stores. Crush up a dunk as best you can, put the powder in a gallon jug with some water, shake it up and let it sit for several hours or over night and then water all of your plants with it. Do this every other week, and within a couple weeks you should notice less of them.
It is good to do use the dunks along with sticky traps and a dusting of DE where ever you see the adult gnats like to congregate. They also find their way up drainage holes at the bottom of the pots and lay their eggs there also, so I work DE into the carpet around the pots. Those that land in it and are exposed to the DE will die eventually.