Does The Reef Tank Need Carbon - By The Reef Geek

There is no doubt that the biggest selling maintenance product in the aquarium industry is Activated Carbon. This long time filter media started as Bone Charcoal 150 years ago, and it’s been keeping aquarium water sparkling clear ever since.

In the aquarium trade, activated carbon is sold in more products than you think. It is the key ingredient in HOB disposable filter cartridges, and is often blended with ion exchange resins, ammonia removers, and other chemical media that makes up hundreds of aquarium products . And of course, it is sold in bulk or pure form for use in canister filters, mesh bags, and media reactors.

Why do we keep using it? Any veteran freshwater or marine aquarist can tell you that it removes odors, removes color, and makes aquarium water as clear as ice. Despite the beauty of your show tank, no one likes to walk into your living room and get a whiff of that “fishy” smell.

There is a lot of confusion about how activated carbon acts in saltwater, especially when it is used in reef aquariums. Here, aquarists are constantly pushing for a more natural filtration approach. But it bugs the hell out of me when I read all the misinformation on the Internet and even on carbon product labels. They preach to use carbon sparingly, like one day or three days a month, or don’t use it all. Folks, Activated Carbon is non-toxic. It cannot be overdosed. It will not remove all the salts and trace elements and turn your tank into some incomplete blend of synthetic seawater.

We all need to realize that our reef and fish-only aquariums are NOT miniature slices of the ocean. They may look that way, but bio-chemically they are an ecosystem that is always on the verge of collapse. Activated Carbon’s job is to remove metabolic wastes, or more commonly called organics. You can employ the deepest sand bed or the largest calcium reactor or a humongous circulation pump, but none of these things will have any effect on organics.

When it comes to organics, the world’s oceans maintain a perfect balance of metabolic waste removal through a series of natural recycling systems. Both the volume of water and the immense surface area provides a home for tens of thousands of species of macro and micro organisms that process these wastes. In the home aquarium, just a small fraction of these organisms can survive. Coupled with an extremely high specimen to water ratio, organics tend to accumulate in closed systems, and can reach concentrations orders of magnitude beyond natural ocean levels. Even with aggressive water changes, these organics can never be diluted enough to mimic the natural levels where our livestock has lived for thousands of years.

Don’t confuse organics with ammonia, nitrites, or nitrates. The bacteria responsible for breaking down these nutrients naturally thrive in all aquariums. Most tanks are nutrient rich and provide lots of food for these bacteria to thrive. Organics on the other hand, consists of complex metabolic compounds including phenols, organic acids, proteins, fats, carbohydrates, and hormones. To break these down, we don’t (and can’t) grow the right bacteria in our aquariums. In fact, detritus on the gravel surface and in the bottom of the sump are organic compounds that have reached such high concentrations that they fall out of solution. These particles remain inert as long as pH, oxygen, and ORP levels stay constant. Any wild swings or disruptions will trigger detritus particles to release these pollutants back into solution, causing an avalanche effect which will fuel a tank crash like there’s no tomorrow.

Where Do Organics Come From?

Creation of organics is a natural process of fish and invertebrate metabolism. It has little to do with the amount of food added to the tank. Reef tanks are especially vulnerable to organics, since corals and invertebrates produce a lot more organics than fish. Coral “slime” is nearly 100% pure organics. When you are mounting a coral or moving things around, copious amounts of sliming results. This slime is torn apart by powerheads, oozes through mechanical filters, and finally winds up being dissolved in the aquarium water. By contrast, coral slime in the ocean is quickly washed away perhaps hundreds of meters away from the coral. It is then consumed whole by other invertebrates or fish or quickly broken down by specialized bacteria and used by plankton as food. Everything is recycled in the ocean. In the aquarium, it has to be removed.

Why Organics Are Bad

While only a few of the organic compounds are directly toxic to marine livestock, they can stimulate the growth of heterotrophic bacteria which robs your tank of oxygen. These bacteria also create carbon dioxide. The result is lower pH and low ORP, which creates ideal conditions for nuisance algae to thrive. Organics can quickly tint aquarium water to a yellow color which greatly blocks blue spectrum light penetration (actinic 420nm). High levels of organics can also tax a protein skimmer to the point where nitrates and phosphate removal becomes minimal.

No one knows for sure the total make up of organic compounds in the marine aquarium and what specific effects they have on different organisms. It had been observed that aquariums with high organic levels experience more fish and coral diseases. There is now firm evidence that organics stunt fish growth. The old mystery of how a fish will grow only as large as its container has been solved. It has nothing to do with the volume of water or the size of the tank- organics accumulation is the culprit.

At moderate organic levels, corals and invertebrates tend to close or cease reproduction. Some researchers believe that there is a direct relationship between high levels of organics and dense populations of disease organisms. The reduction of naturally occurring organics ultimately leads to improved water quality and healthier specimens. Activated Carbon is the most effective and easiest method of removing organics from aquariums.

How to Tell if Your Organics Levels are High

The tell tale signs of high organics in marine aquariums include (1) Persistent hair algae problems despite low nutrient levels, (2) Some foaming in the sump or in the corners of the tank, (3) An oily film or cloudy layer on the water surface where even a tank overflow can’t seem to get rid of all of it, and (4) small growths of Cyanobacteria spotting on rocks and the gravel.

How Activated Carbon Works

Activated carbon is a unique product that starts out as nut shells, wood, or coal. It is pyrolysed in a 750°C oven which cracks the material and creates millions of micro pores on the surface and though the interior of each grain. The surface area of these pores are immense. One gram of granular activated carbon has 5,300 square feet of surface area. By comparison, a tennis court is 2,800 square feet. It is not only the large surface area of carbon that attracts organics, but there is an electrical charge involved that draws organics to the carbon.

Choosing Activated Carbon

In the aquarium trade, bulk activated carbon is sold in granular and extruded forms. Extruded products appear as pellets and spheres. These carbons are more rugged and can take tumbling in media reactors without breaking apart. They also tend to have less dust. However, extruded carbons have less surface area than granular carbons, so more product will be needed to achieve the same results. Granular carbons are softer and are more dusty. Dust level has nothing to do with the quality or effectiveness of carbon.

There are lots of brands of activated carbons to choose from. The quality ranges from downright detrimental to excellent. Avoid any product that uses the term “charcoal” or “char” in its name. These products are not activated and are limited to removing heavy metals and odors. There are ineffective against organics. They also contain calcium phosphates- which act as a nutrient for algae growth.

Activated Carbon has gotten a reputation of adding or leaching phosphates back into the water. This is only partially true. Activated Carbon can be made in two ways, either by Physical Activation or Chemical Activation. Physical activation used CO2, oxygen, or steam, and contains no phosphates. Chemical activation uses phosphoric acid and zinc for activation. If you buy the latter, then adding carbon will also add phosphates to your water. You are better off not using carbon at all then using a phosphate washed product.

Here’s a guide on what to look for when buying activated carbon:

► Look on the product label for information about the carbon. If the label talks about the carbon process of using steam, oxygen, or carbon dioxide, then it is truly phosphate-free and won’t leach phosphates into the water. Some carbons are simple marked “Phosphate-Free” which indicates a steam activated process. If the label does not mention phosphates, doesn’t tout the activation process, or requires rinsing to minimize phosphates, it is likely a low grade phosphor-washed carbon that should be avoided.

► If you use your carbon in a media reactor or tumbler, buy an extruded or pelletized carbon. It won’t break apart when the grains bang into each other. For use in canister filters or mesh bags, use granular carbon. It will give you more surface area- albeit at the cost of being softer and more fragile.

► Ash is an inorganic material that is left behind after the activation process. Look for carbon that is marked as low ash content or one that states “Does not affect PH”. High ash content can cause a significant rise in PH when first placed in the aquarium. This can cause undue stress on the livestock. I have personally seen pH values climb within minutes from 8.0 to 9.5 pH with some carbons. All carbons contain some ash and a thorough rinsing in fresh water will remove most of it.

► Quality brands of activated carbon will feature other parameters, such as Iodine Number below 600, Molasses Number above 400, or listing pore size in Angstroms. These are all signs of a quality manufacturer that has nothing to hide, and is offering a superb product.

BRAND	Average	Good	Excellent
Aq Pharm Black Magic®	█
Kent Reef Carbon®		█
Boyd Chemi-Pure®			█
Hagen® Fluval® Carbon			█
Hydor Prime®	█
Lifegard® Pelletized	█
Marineland Black Diamond®		█
ROWAcarbon®			█
Seachem Matrix®		█
T.L.F. Hydrocarbon®			█
Warner® Granular			█

How To use Activated Carbon

► For ongoing maintenance, I recommend 1 cup per 60 gallons of water. This is a bit higher than most suggestions, but using more carbon works faster and lasts longer. Double this amount for tanks with obvious signs of high organics or first time carbon use in poorly maintained tanks.

► Filter the water mechanically before it reaches the carbon. Particles greater than 100 microns in size will take a toll on the life of the carbon.

► Despite popular belief, carbon does not need to be placed in a canister filter or a compartment where all tank water passes through it. Dropping a mesh bag full of carbon into the sump works fine. This is because carbon works by electrically attracting particles- it is not an inert mechanical filter. Studies have shown that bags of carbon in a sump with moderate flow removes substantial quantities of organic pollutants, medications, and heavy metals. Actual performance depends on the flowability of the bag material. It is most effective if you use a media bag with the largest possible hole sizes but small enough where the carbon cannot escape.

► For the average marine fish aquarium, carbon will last 6 weeks. Reef tanks produce more organics than fish-only tanks, so 4-6 weeks is a workable limit. If the water is not mechanically filtered or the aquarium shows signs of nuisance algae, you will need to adjust the useful life or increase the amount of carbon.

► There is no effective way for the aquarist to either recharge carbon or measure its rate of exhaustion. I have experimented with the Salifert Organics Test Kit to measure carbon life, but I was unsuccessful because the range of the test kit would not allow me to measure steady declines over time. Don’t re-use carbon or try to clean it. Recharging carbon requires a specialized high temperature/low oxygen oven that would be prohibitively expensive at this small scale. The best solution is to replace the carbon at 4 to 6 week intervals.

Activated Carbon Myths and Misconceptions

► Carbon removes trace elements- Carbon has a greater affinity for organics than trace metals, but it will remove some trace elements. On the other hand, both protein skimming and natural consumption of trace elements by tank specimens will remove significantly more trace elements than carbon. Aquarists concerned about depleted trace elements should be using a trace mineral additive- whether or not carbon is used. Two excellent products for this are the Sera Strontium Complex and the Seachem Reef Trace products.

► Carbon will leach organics back into the water False. Once all the carbon pores are saturated, bacteria slime and detritus will accumulate on the carbon grains, turning it into a weak biological filter with the organics locked in the deeper layers.

► Carbon should be used only a few days a month False. This myth was likely started by activated carbon’s ability to remove yellow tinting and odor from the aquarium within the first 48 hours of application (or perhaps manufacturers who want to sell you more carbon). The higher concentrations of organics are colorless and odorless and require more contact time for removal. Another complication of part-time carbon use is storage and reuse. Once the carbon is removed from the aquarium it will continue removing contaminants from the air. Placing the damp carbon in a sealed plastic bag doesn’t work either, as the damp carbon becomes exhausted servicing die off in the stagnant aquarium water stuck to the grains.

► Spilled carbon causes harm to the aquarium False. Carbon granules that are accidentally spilled into the aquarium will quickly become saturated with bacteria slime, having the same biological effects as a grain of gravel. It may look ugly, but it is totally harmless.

As we have seen, the use of Activated Carbon is an important part of maintaining a healthy marine or reef aquarium. It is the only filtering media that can remove substantial amounts of metabolic wastes (organics), which accumulate over time and can prevent secondary water quality and health problems in specimens. Because of the phosphate issue in lower quality products, it is better to spend a little more on a quality carbon than use any carbon at all.