if they are little black ones that seem to come in biblical numbers and hang around the soil and under the light canoy then they are fungas gnats.
had same problem last grow.
beat way to get rid of them, by experience, is to:
dose with Gnat Off to kill larvae - goes in feed water or nutrient solution so does not affect bud taste
hang some of those sticky traps under lights to kill adults
put and or clay pebbles wver soil surface of pots to deter adults from burrowing and egg laying.
mine were sorted in a week.
important you do something, as larvae will cause severe damage to plant roots
good luck.