Hi Hoolio,
Welcome to MR! I perform similar maintenance on my canister filter as stated by jacuglietoo, although I run mine on freshwater tanks. I run my carbon for a month before changing it out. Yes, you should remove the old carbon and replace it with new. This is because the water polishing capabilities of the carbon are used up over time. How long is carbon actually useful as a water polisher? One week, one month, or more? Well that can depend on the tank itself and other factors that an in depth scientific study could (and I am sure has) determined. However, to keep things simple, and to keep a fresh supply of new carbon running on my tank, I replace half of the carbon on bi weekly intervals. This ensures that at least some, if not all, of the carbon in my canister is doing its intended job.
The mechanical filter pads should be cleaned with old tank water. I wring the pads out in a bucket of old tank water during my water change routine. You do not want to use tap water because you will undoubtable introduce the tap water into your tank and that is not good. Tap water contains chlorine and chloramines that kill bacteria (the beneficial ones too), and can also contain metals, phosphate, etc. Also, I reuse my filter pads until they are ragged or so clogged that wringing them out no longer cleans them well enough. I wring them out every two weeks.
Finally, you should do a thorough cleaning of the entire canister every three months. The mechanical filter pads only collect so much detritus. Eventually there will be an accumulation in the bottom of the canister itself that needs to be cleaned. I rinse the actual canister out in the sink, making sure to wipe it dry before filling it with the media again. You can also clean the other media you use at this time (i.e. ceramic rings used bio filtration). Again, you should rinse this media in old tank water.
Well, I hope this helps. If you have any other questions let us know.
