Small frequent changes are the best for a small tank in my opinion. I would try a weekly 1 gallon change and then check your levels like you are doing. Once you start adding more critters to the tank you will obviously be producing more wastes and might have to either up the frequency or size of changes.
For reference I used to do a weekly 5 gallon change in my old 30 gallon tank. I started battling water parameters changes so I upped to 3 gallon changes twice a week to try to stay ahead of it.
John
"Critics are men who watch a battle from a high place and then come down and shoot the survivors." Ernest Hemingway