Water less, let them dry out as much as you can without killing the plants. After put an inch or two of sand as a top soil. This will stop any gnats in the soil from getting to the surface.
You can also use diatomaceous earth food grade, this will kill many bugs and is safe for humans so long as you arent huffing the stuff. It cuts their exoskeletons and they dry out and die of dehydration.You c line your yard with tis stuff to kill any and all bugs that want to cross that line of death
If i had pots with a few holes on the bottom i would temporarily tape them to stop adult gnats from getting in through the bottom.
Killing adult gnats flying around with your hands when you can, clapping, helps also.It adds up eventually with all your other traps.
Also yellow sticky paper, gnats are attracted to Yellow color
You could make a home made natural trap of apple vinegar and water simply in a bowl, they will drown in it.
Fungus Gnats generally do the most damage to clones and seedlings. Generally adult plants can soldier through a gnat infestion, but fresh clones and especially seedlings can be decimated by them