Changing the filter cartridge isn't as necessary as the package states. By constantly replacing your cartridge, you are throwing out a lot of good beneficial bacteria and setting your tank up for a mini- cycle, which isn't good.
A new pad gives you the benefit of fresh carbon, but that's only useful if you are trying to remove something like medication from the water. Otherwise, there's no need to change it every 30 days. Just give them a quick rinse in decholoinated water, or old tank water and you're good to go.