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Dear Aquaworld,

I have spoken to many people who insist that you must use carbon in your filter. I have discus which were purchased from you at your store a while back. I have never used carbon with them and actually never will. What are the advantages if any that come with using carbon. And after a while if not changed will it leach bad things back into the water which it had previously pulled out?

Fair Oaks, CA USA


Dear Phil,

I was just asked this question at the Marine Aquarists Roundtable of Sacramento (MARS) meeting a few nights ago.  No, you do not have to use carbon to have a healthy and thriving aquarium.  In fact, the use of carbon can sometimes do more harm than good.  Carbon removes a lot of different elements from the water, some bad as well as some good trace elements.

My use of carbon is restricted to use for specific purposes.  I only use carbon for removing medication, and removing tannins (the tea color).  Once the carbon has been in the aquarium system for a few days I remove it and do a large water change, and replace any trace elements that may have been removed by the carbon. 

If you have a planted tank or reef tank, and you use carbon in the system, the carbon will often strip out many of the plant and reef trace elements you add to the aquarium.  If you leave carbon in the aquarium system for a long time it will eventually become biological filter media.  Once the carbon has been exhausted (can not remove any more elements from the water) it can in time leach back into the aquarium elements it had removed from solution through the biological breakdown of the carbon.  This process is very slow, and if you are doing regular water changes it is unlikely that it would have any adverse affect on the system.

Tony Griffitts

Published - 20070220