i have a 5 gallon bucket of mosquito bits, they will not completely erradicate gnats, i throw that shit in the pots by the handfull, gnats just dance on top of it. mosquito bits are bti. if you must use bti, for better results run alongside hypoapsis miles, but alone, they multiply too fast. bottom line contain them, cover your pots so they can be completely removed when time comes. if not you will always have a presence of gnats in your garden, you know, that gnat flying around in ya face every now and then.
PEACE!
PEACE!