Can you buy a product called a Protein Skimmer that pretty much allows you to keep your tank safe and not have to change the water at all....i think they run at about 100 bills
It is the popular opinion that all salt water tanks need a protein skimmer, they will cut down on your need to change out the water but nothing will eliminate that need.
My QT is only 29 gallons and I ran a skimmer on it for a LOOOOONNNg time... I had to stop when the skimmer broke. Now I do a 5 gal water change every other day.
If you do enough water changes, are below your bio load capacity and do not yet have the scum floating on the top of your water, then you prolly don't need one...yet.