Just recently I came across gnats hanging out underneath my lights and the inner walls of my tank. At first I just swatted them away thinking not too much of it, but then a few weeks later I started realizing that they've started breeding and 5-6 larvae were on the inner walls of the tank. I've done a 80% water change and within a week I'm right back to where I started (Iv'e done this twice so far). What can I add to my water that will take care of this annoying problem, can salt help?

"What can I add to my water that will take care of this annoying problem"
Fish. Why aren't yours eating the larvae? What kind of fish do you have in that tank?

"the gnats and larvae aren't in the water they are on the inner walls of the tank where it's moist enough for them to live off the water without actually being in it."
oh. Well you could try this: Take a paper towel and wipe off as much of the damp glass as you can, crushing any larvae you find. Then spray the glass lightly with an aerosol cooking oil like Pam. The bugs can't grip it.

@ natalie265 did you read the replies as well?