Looks like Pro-mix or something. What kind of grow method is this anyway? Nutes on every watering with HP medium? If so, treat it more like coco. Keep it all moist because if it dries knuckle deep, it will be just as dry where the roots are.
If you're doing soil on the other hand, you shouldn't just dribble water on the surface around the plant either. It should be moist all the way through after watering.