[The old man]

I have two Eheim Classics and after the first two weeks I don't use carbon at all. If you got planted tanks I'd recommend for the classics using what comes with them then after a couple weeks get rid of the carbon pad and just use the Ehfimech and ehisubstat and a fine filter if you stir up the substrate when changing out plants. You can also use bio balls or something else. I clean mine about every three months by just removing the filter and turning the bottom spout down in the sink and pouring two or three gallons of declorinated water thru them till water clear coming out the bottom. Good time to clean the impeller also. I doubt I'll ever need to change the media except the fine filter if using one.