FYI, marine set up do not use filter but protein skimmer to remove organic waste. Water change are mainly done to remove water that are 'dirty' due to high level of unwanted parameter and also to introduce needed elements into the water column. The protein skimmer do not remove unwanted compound such as nitrates n nitrites as these are in the water column itself and to extract these require something to consume it or to remove part of the water containing these compound in order to lower their percentage in the water. To prevent these compound from increasing in the tank, adequate water movement is needed in the display tank by the use of strong wavemaker in order to keep the organic waste suspended in the water which will then be moved to the overflow and down to the sump where it will be processed by the protein skimmer.
A good way to achieve this is to match the flow coming down from the display tank to the skimmer pump flow rate. A higher flow than what the skimmer can pull is not a good practise as the remaining water that pass the skimmer will return back to the display tank and feed the algae or let the organic waste to rot.
A denitrator is not the final solution to the problem of elevated unwanted compound level. It is not a set and forget type of equipment and could bring harm to the livestock if the owner are not well aware of their equipment function. Not monitoring this equipment from time to time will bite back the owner in the future.
Hope this helps!