I have a refugim full of cheato, which the lights are on for approximately 15 hours a day.
Other than that, i run a Deltec AP851 skimmer, which is not exactly over-sized for my tank.
I try to do water changes once a week, at least 50 litre.
There are many ways to lower No3, i am sure a denitrator does help. If not get a more powerful skimmer or change water more frequently.