Why would you ever have to treat you tank??? If you've set up and follow a sound tank maintenance routine which includes changing half the water and servicing your filter equipment every week, there won't be a reason for treating your tank.
You don't need to use much carbon in your filter. I use a small pad to keep odors down. The importance of carbon in the filter is overemphasized. Large, weekly water changes do a lot more for your tank than carbon.
If your tank is cloudy an extra HOB
is helpful. I use one occasionally and put just polyfiber pads in the filter. The polyfiber will filter out the smallest particles and gets the tank water crystal clear in just a day or two.