I'm not sure what you're describing here, but ANY type of discharge from a bird's nostrils, whether it's clear or not, is a sign of either a sinus infection/issue or an upper respiratory infection/issue. The reason that this is a big deal is because, and I'm sure you're aware, birds hide any and all outward signs/symptoms of illness and pain for as long as they can, it's a natural, innate survival instinct that protects them and their flockmates from predators who target weak, sick birds. So when it comes to both Sinus and Upper Respiratory Infections, a completely clear discharge from their nostrils is a very early sign; The same thing goes for a white discharge/film from or in their mouths or around their beaks/nostrils as an extremely early and first sign of a fungal/yeast infection. So you may have actually gotten lucky and been able to see this very early sign, as opposed to how it usually goes, where your bird is sick for weeks or months and you have no idea until they are extremely sick and start showing other, more serious signs and symptoms. So it would be a very good idea for you to take him to his Certified Avian Vet or Avian Specialist for a simple culture so that you catch it very early and get him on the correct medication for whatever microbe is causing the infection, rather than waiting until he's really sick and requires much more invasive and much, much more expensive testing and treatment further down the road.