Nematodes.

Nematode - Wikipedia, the free encyclopedia

Order from any greenhouse supply place for about $10 for enough to cover 2-3000 sq. ft. They will eat all the larvae. Water all the plants in your house with it, the fungus gnats will travel and lay eggs in all your plants. If you catch them early enough, a single yellow sticky trap can eliminate them.

This is the easiest of all pests to get rid of, they don't do any damage unless you let them get way out of control.