How long does carbon last in an aquarium filter?

Carbon is a chemical filter media for aquariums which removes dyes, odours and impurities from the water. It uses adsorption, meaning it can attract molecules to its surface where it will then adsorb and hold the impurities until saturated. When carbon is saturated, throw it away and replace with new. 

Every aquarium is different and unlike phosphate remover, it’s hard to test the water to get an idea of when carbon is spent and no longer useful. So much more simply we just change carbon on a monthly basis

Carbon can come in granular or pellet form, or even impregnated into filter pads. Activated carbon is exposed to higher temperatures during manufacturing, making it more porous and more effective. 

Carbon is most commonly used to make aquarium water crystal clear, by removing tannins from bogwood and discolouration from fish food, fish faeces and biological process, which can make water go yellow. 

But it can also remove chlorine, and traces of medications. That’s why you should remove carbon when treating your fish for disease. It will soak up the medication and make it less effective. 

Change filter carbon every month, in conjunction with a filter clean and a partial water change. Carbon is suitable for use in all aquarium and ponds including coldwater, tropical and marine. 

Carbon removes impurities and clears water

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Jeremy Gay is an author, lifelong fishkeeper, and aquatic specialist. He's a former editor of Practical Fishkeeping Magazine, UK editor at Reefbuilders, a former aquatic store manager, and has collected fish in Sri Lanka and the Amazon. He's been on tv and radio, contributed to Koi Carp and Gardeners World magazines, been a product tester, a judge, and a product developer. Jeremy is here to guide and advise you on all things tropical, pond and marine, from set-up to stocking, health, feeding to breeding, as well as solving many common fishkeeping problems along the way.


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