For clarification, you can spend a force point to remove a Dark Side point. Using a Force Power with the Darkside descriptor is considered a major Transgression.
Since he is a Padawan, he will probably get a rebuking by council and sent on a mission that will help him control on his anger and temptation. The Jedi Council can't afford to lose a good warrior. Mechanically, he is doing nothing wrong.
But if you want to stress the danger of the Darkside, then you should have him become the interest of dark forces. Perhaps a very powerful Dark Force wishes to turn him and future adventures put him in danger of calling on the Darks Side more often they he wishes. Lost of good story to play with here.