Fungas gnats. To kill the adults get a spray with pyrethrins (made from chrysanthemum flowers) and cover the soil with it. Fox Farm "Don't Bug Me" is an example. Using yellow sticky strips close to the soil can also catch hundreds of adults and helps the cause. Next, drench the soil on the next few waterings with a BTi solution (eg. Gnatrol). That kills the larvae eventually. Expect to fight them for at least a week or two this way. BTi is Bacillus thuringiensis isrealensis that is also in mosquito "dunks" and some other mosquito killer formulations. Good luck.