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A guide to using Activated Carbon

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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.

Written by Pete (Killi)

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