I agree with ali, I dont think it's the end of the world if you havnt had a water change in a FOWLR tank with that bioload.
However you may want to decide a water change schedule and stick to it. Once or if you start adding corals, at that point you'll probably want to change it more often then every 6 weeks. either weekly, bi weekly or monthly depending on your own schedule, bioload increase and the demands of your tank.