Don't ever change all of the filter media at once!! Now you're for sure forcing the tank into a mini cycle
Rinse the filter pads in tank water (that you obviously remove from the tank first) during water changes, once a week or every two weeks. It's really important that you take care of the filter media or you'll have problems with ammonia all the time. When you notice the filter media getting sort of softer and more "used" looking you should change only half the filter media then and the other half after a month.