Carbon Use In Saltwater: The Myths and Facts

By: Michael Phife


The use of carbon in saltwater aquariums has been a very controversial subject whenever you search for the topic online. There are so many conflicting debates between forum members on whether or not to use this type of media, and a lot of rumors spreading throughout said forums about carbon being good or bad for the overall health of a saltwater tank. As an aquarium hobbyist, as well as someone with an understanding of Organic Chemistry, I am going to break this entire ordeal down for you guys, in order to resolve this topic once and for all!


The Myth

So the myth about why many people say to stay away from using carbon use in saltwater compared to freshwater is as follows… Carbon filter pads (or media bags) are theorized that they engulf the salinity that passes through the filter, and thus putting carbon into the water itself. The reason people are saying this is bad is firstly, the myth that carbon removes salinity from the aquarium; therefore bringing your tank’s salinity below the needed threshold. And secondly, the idea of adding a chemical into saltwater that should not be there naturally, as deemed by various aquarium hobbyists. The idea is to keep your aquarium as free from outside chemicals or compounds as possible, and only keeping the vital minerals in the water such as calcium and magnesium. But if carbon is purely beneficial to freshwater, then why is there so much fuss about using it in saltwater?


The Facts

The answer is that carbon is NOT harmful to saltwater. When using a mechanical filter for saltwater tanks, the water passes through the filter and media just like it would with any other type of setup. However, it does not strip away any salinity in the water, or if it does then it is such a minuscule amount that it cannot be seen on a refractometer when tested. When water passes through the filtration, the ammonia, nitrites, nitrates, and any other organic waste is being trapped into the filtration pad itself. Not only that but the carbon is then purifying the water when expelled back out into the tank, and gives the water a very pristine look. I have used carbon filtration in two out of four of my aquariums (one of them being my most recent aquarium), and I have had absolutely no detrimental effects with doing so. Not only has my tank flourished with using carbon, but the water is so clear that it looks as if the fish are floating in air.

Carbon filtration. Courtesy of

How to Use Carbon in Your Aquarium

Carbon is used just like it is for any other aquarium! If you wish to add on a hang on the back filter, then the filter pad or media bag can be stored inside of it just like a freshwater setup. A media bag can also be placed in overflows, or refugiums in one of the chambers. Treat this setup like you would any other basic tank, it does not have to be difficult. Usually people like to over-think how they should map out their aquarium hardware or filtration, but make it easy on yourself. If you run a sump or refugium, then by all means put the carbon in the designated chambers that way. If you run an HOB, the filter pad should not be seen as your enemy. Keep it in the filter, there is absolutely no harm in this. It has been mind boggling that so many people who have done saltwater aquariums for years are so reluctant to run carbon in their tanks.


Maintenance and Etc.

The only thing you will need to do for maintenance is rinse the filter pad off in excess aquarium water or distilled water when it needs to be cleaned. Do not use tap water!!! I have seen so many people run their filtration through the tap and then later ask why their fish have died. Rinsing the filter pads off in tap water traps chlorine into the carbon, and then expels it back into the aquarium which poisons the fish. Aside from that, filtration pads should be changed out once they begin to erode or lose effect. For me, they can last close to a quarter of a year with moderate feeding and no overstock of fish in the aquarium. As long as you are conscious about what you are doing then this entire method of carbon use is perfectly healthy for your fish buddies and the longevity of your aquarium.