Changing The Ceramic Media Cartridge

What is leading to you wanting to change the cartridge Ally?

The company is just trying to sell more media to be honest with you. 

You are absolutely correct in that changing the media without building up beneficial bacteria on it would cause you to have to essentially re-cycle the tank. Problem is there is little motivation for the bacteria to spread onto the new media at present as your old media is taking care of the wastes in your tank already.  Put another way. You won't grow twice as many bacteria by having twice as much media because you haven't given the bacteria any more food than before.

It is interesting that you mention the media looking green as this might indicate algae growth, are you having problems with algae in the rest of the tank? Can you describe in a little more detail why you believe the media to be 'dirty'?

Also is your old media still in the filter? Id move it back in there if its somewhere away from the filter flow at the moment...