Hey yoyo,
It looks like you have the start of a salt build up happening. I would suggest a flushing with straight water your next watering. Let the run off flow out until it's clear instead of yellow/brown. The small flies are probably soil/fungus gnats. They're more of an annoyance than a potential problem but don't let em get any worse.
Keep your area clean of any standing water or dead debris.
Look into some sticky strips or sticks to catch the adults flying around the soil . It should cut down their population enough.

First things first though, correct the salt build up in the medium by flushing and restarting your nutrient regiment.

Hope this helps,
Bob.