Activated Carbon

Activated Carbon Uses

Carbon has been used for centuries to purify drinking water.

In our saltwater aquariums, activated carbon adsorption serves to remove dissolved organic compounds (DOCs) and phenols that cause yellowing of the water. It also removes some toxins exuded by corals. Bacteria will also colonize the pores on the surface of the carbon beads if it is left in the tank long enough, eventually turning it into a biological filter.

Activated Carbon And Medications

Activated carbon will remove medications from quarantine tanks very well. (You are medicating sick or diseased fish only in quarantine tanks, right?). Once a sick fish is cured, it shouldn’t be removed to the main aquarium immediately. Removing the medication from the water with activated carbon will allow the fish to remain in quarantine for a few more days, to watch if symptoms reappear.

Seachem Matrix Activated Carbon

Seachem Matrix Activated Carbon

It should be noted that activated carbon is at its most efficient in the aquarium for the first 48 hours after which its efficacy tapers off dramatically.

Activated Carbon Placement

In a saltwater aquarium, activated carbon should be put into a mesh bag and placed in a point of good flow in the sump. If a sump is not part of the aquarium system, most hangonback filters will have compartments for activated carbon. For even greater efficiency you could also put carbon into an aquarium canister filter or better yet, a fluidised reactor.

A fluidized reactor such as Two Little Fishies’ PhosBan Reactor provides a simple solution for fluidizing activated carbon.  Maintenance and changing out the carbon is also made easy with the simple screw-on seal on the TLF Reactor.

Activated Carbon And Trace Elements

Activated carbon will also absorb trace elements rapidly from our saltwater aquariums has been sometimes blamed for the bleaching of SPS and LPS corals, as it quickly adsorbs trace elements. Iodine is one of the important elements that is quickly absorbed by activated carbon which is why it is important for marine aquarists who use carbon on a continual basis to dose iodine or stabilized iodide regularly.

To avoid the sudden rapid depletion of trace elements, it is better to replace a small amount of carbon every 2 weeks. The impact on trace elements will be much less compared to using a large amount of carbon all at once and replacing it once a month.

Amount Of Activated Carbon To Use

Recommendations for how much activated carbon to use differ wildly.

But a good rule of thumb for the routine use of a small amount of carbon would be 2 to 4 heaping tablespoons per 50 gallons of aquarium water. Depending on the number of fishes and the bioload, this amount can be adjusted upwards accordingly.

Give the carbon until the next day to give a result, before deciding to increase the amount. This is especially true if trying to eliminate yellowing in the water. Too drastic a change in water clarity can shock the corals with the sudden increase in light penetration.

It is a good idea to rinse the carbon only in reverse osmosis or deionized water before use to remove residual ash. Using ordinary tap water will cause the carbon to absorb the impurities in the water.

Seachem’s Matrix Carbon

As far as brands of activated carbon, I have used and highly recommend Seachem’s Matrix Carbon.

Used in small amounts and changed out every 2 weeks, Matrix Carbon efficiently removes organics and phenols that causes yellowing in the water.  It also leaches virtually zero amounts of phosphate, as we will discuss later in this article.

Activated Carbon And Phosphate

All activated carbon will leach small amounts of phosphate, some brands more than others. To find out if your favorite brand of carbon leaches significant amounts of phosphate, soak 50ml of carbon in about 300ml of de-ionized water for 24 hours and test the water. Avoid any brand that gives a phosphate reading greater than 0.25 ppm in 300ml of water.

Activated Carbon — Some Personal Observations

I have noticed that some leather corals, zooanthids, palythoa and xenia tend to close-up for a day or two when even a small quantity of activated carbon is introduced. This could be due to the carbon stripping certain essential minerals from the water. This is no reason for alarm as corals usually re-open after activated carbon’s 48 hour efficacy period.

But it is for this reason that I now use Boyd’s Chemipure, a mixture of activated carbon and ion exchange resins  instead of plain activated carbon as it seems to have no negative impact on livestock in the aquarium at all.

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