Aquarium Filters with Activated Carbon

Using Activated Carbon in Aquarium Filters

For decades, activated carbon has been used in home aquariums, and it is still the most popular filtering media. The value of utilizing activated carbon in has grown as new types of and media have become accessible. Some experts feel it should be used as a standard medium in all filters. Others say it should only be used for specific purposes, while others believe it should be phased out entirely.

It's vital to understand that when carbon is utilized in an aquarium filter, it's quickly depleted. As a result, if activated carbon is used on a frequent basis, it should be replaced on a regular basis. It is of little use otherwise.

What Is Activated Carbon?

Activated carbon is manufactured from carbonaceous material that has been heat-treated at extremely high temperatures to create a large number of small holes and hence considerably increase its surface area. The filter medium can capture a high amount of material thanks to its small pores and huge surface area, making it excellent for eliminating contaminants from both air and water. Different techniques of producing activated carbon yield different types of material appropriate for various applications. GAC, or granular activated carbon, is the most common kind used in aquariums. Activated carbon can have the following forms:

  • BAC, or bead activated carbon
  • EAC, or extruded activated carbon
  • GAC, or granular activated carbon
  • PAC, or powdered activated carbon (also available in compressed pellet form)

There are also several carbon sources, each of which can result in a variety of pore diameters. Activated carbon is made from a variety of materials, including coal, coconuts, peat, bamboo, and wood. Bituminous coal is the finest supply for aquariums.

What Activated Carbon Does

Chloramine and chlorine, tannins (which color the water), and phenols are among the dissolved pollutants that activated carbon adsorbs (which cause odors). It will prevent the water in your aquarium from becoming yellow over time.

It is critical to recognize that activated carbon does not eliminate a number of significant poisons. It does not, for example, remove ammonia, nitrite, or nitrate. As a result, it is ineffective in removing toxins during the initial tank setup. To treat increased ammonia, nitrite, or nitrate levels, water changes or other techniques must be employed.

Heavy metals, such as lead or copper, are also not removed. If your water source has heavy metals, use a water treatment product before putting the water into the aquarium.

Activated Carbon and Medications

Many drugs used to treat fish illness will bind to activated carbon. As a result, all carbon in the filter should be removed before treating ill fish with drugs. It is OK to return activated carbon to the filter after the treatment has been finished. Any remaining drug in the aquarium water will be removed by the carbon.

Placement in Filter

If activated carbon is exposed to a lot of aquarium trash, it will soon lose its potency. As a result, carbon should be added to the filter after the mechanical filtration media. Maintain in mind that the activated carbon will not work if you do not and debris builds up in the filter.

Changing Activated Carbon

Because activated carbon binds to the impurities it removes, it ultimately gets saturated and unable to remove any more. As a result, it must be updated on a regular basis—once a month is generally adequate. The tank will not be harmed by longer periods between replacements, but the carbon will progressively lose its capacity to remove pollutants from the water. If the water in your tank has become yellow or has an odor, it's time to replace the activated carbon.

Myth of Recharging Activated Carbon

Activated carbon recharge stories abound. Some even include detailed directions, which usually include baking the carbon in your oven. These tales are legends. In your kitchen oven, the temperature and pressure necessary to replenish depleted activated carbon are insufficient. When replacing activated carbon, it's best to get new carbon from a fish store, and preserve unused activated carbon in an airtight container because it can absorb scents and pollutants from the air.


You may have heard that when activated carbon reaches its limit, it begins to leak some of the absorbed materials back into the water. This is not a true statement. De-adsorption, while technically conceivable, necessitates chemical changes that do not occur in an aquarium.

However, some activated carbon manufacturing procedures might result in the in the final product. Phosphate already present in the activated carbon might seep into the aquarium water in this situation. Some activated carbon products declare whether or not they are phosphate-free.

Remove the activated carbon completely if you're having problems with continuously high phosphate levels and can't pinpoint a cause. Perform routine tank maintenance for a few months to observe if the phosphate level stays high. If it remains high, the carbon was most likely not the cause of your excessive phosphate.

Cautions With Carbon

Using activated carbon in your filter is a nice idea, but it isn't required. You don't need carbon if you're testing your water, conducting frequent partial water changes, and dechlorinating the replacement tap water. It's only an extra cost because the carbon has to be replenished every month.

The helpful bacteria that convert ammonia to nitrite and eventually nitrate will find a home in the carbon in a recirculating filter system. When you replace the carbon every month, you are removing a piece of the biofilter, and it will take some time for the new carbon to produce helpful bacteria. If the carbon media makes up a considerable portion of your filtration system, each change will result in the loss of your biofilter. After introducing the additional carbon, an ammonia surge might ensue. To avoid this, fill the filter with enough sponges, beads, bioballs, or ceramic beads to function as the major media for the bacteria that form the biofilter.

Powder activated carbon has been observed to blow into the aquarium as a fine dust that becomes caught on the fish's gills when utilized in the filter system. There have been reports of fish dying after using powdered carbon that wasn't adequately contained in the filter's media bag. Carbon particles were discovered in the gills and fin tissues of the deceased fish during necropsy. This problem may be avoided by using bigger pelleted or granular activated carbon and washing the dust off with distilled water before adding it in the filter chamber. Rinse the new carbon with distilled or deionized water to avoid it adsorbing chlorine from the tap water before it goes into your filter!