I recently purchased and installed an External Canister Filter in my aquarium which includes a filter stage with little bags of charcoal media.
Clearly I need to replace this at some interval because the manual tells you how to replace it and I see them selling it at the store, but the manual says nothing about the frequency or determining when the charcoal media needs to be replaced. I'm assuming I don't wait until it is gone, but does it change color or something to indicate it is used up? Will my tank start getting more algae when it stops working? Can I tell by smelling it? Or do you just have to do it at a specific time interval? If so, how do I know what that time interval should be.