best tips for plant food + gnat control

i need to turn over a new leaf (haha) and start taking better care of my indoor plants: i keep noticing a gnat here and there but not many .. although that's probably because i keep forgetting to water things. also, i have never used a fertilizer/plant food in any of my indoor plants. and besides watering, i know they could do better.

Is there a plant food out there that also helps control gnats?
i know about mosquito bits, i've used it, it works. but can i mix that water with plant food water?
what's your routine to feed and protect your plants?