Originally Posted by BBradbury
The carbon stuff isn't needed. Save your money and put more effort into removing and replacing the tank water. Small tanks up to 30 gallons need half the water changed every week. The larger tanks can typically go a couple of weeks between the 50 percent changes. The water change will safely remove any toxins in the water and does a much better job than the carbon medium.
With respect, it is not the size of tank that governs water changes, it is bioload. For.an extreme example, you wouldn't need to change half the water weekly in a 30g if you kept one neon in there!
Activated carbon can still help with water clarity as it adsorbs tanins and dissoved organic compounds that stain the water that yellowish colour. In marine tanks, protein skimmers are used instead, although skimmers can also be used in fresh water tanks.
It isn't really necessary, but it isn't a bad thing either.