Using Activated Carbon in Aquarium Filters

Activated carbon has been a staple in home aquariums for decades, maintaining its status as the top-selling filtration media product. Yet, what does it actually remove? With the advent of new filters and media, opinions differ: some advocate for its continuous use, others suggest it for special circumstances, and some argue against its use altogether.

Remember that activated carbon depletes quickly in aquarium filters. If you choose to use it continuously, replace it regularly; otherwise, it becomes ineffective.

What Is Activated Carbon?

Activated carbon is created from carbon-rich materials that undergo high-temperature heat treatment, which forms numerous tiny pores and significantly increases its surface area. These pores enable it to trap a substantial volume of pollutants, making it effective for cleaning air and water. Various creation methods yield different forms, suitable for specific uses. In aquariums, the most common form is granular activated carbon (GAC). Other forms include:

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

The carbon source also impacts pore size, with materials like coal, coconuts, peat, bamboo, and wood used to produce activated carbon. For aquariums, bituminous coal is the preferred source.

What Does Activated Carbon Do?

Activated carbon adsorbs several dissolved contaminants, including chloramine, chlorine, tannins (which discolor water), and phenols (which cause odors). It helps prevent aquarium water from turning yellow over time.

Does Activated Carbon Remove Ammonia or Other Toxins?

Understand that activated carbon does not remove crucial toxins such as ammonia, nitrite, or nitrate. Consequently, it doesn't assist in toxin removal during initial aquarium setup. Use water changes or alternative methods to manage elevated ammonia, nitrite, or nitrate levels.

Heavy metals like lead or copper are not removed by activated carbon. If your water contains heavy metals, treat it with a water conditioner before introducing it to the aquarium.

Activated Carbon and Medications

Activated carbon can adsorb many medications used to treat fish diseases, so remove all carbon from the filter before medication treatment. Once the treatment is complete, you can safely reintroduce activated carbon to remove any residual medication from the water.

Placement in Filter

Activated carbon quickly loses effectiveness if exposed to debris. Place carbon after mechanical filtration media in the filter. To maintain effectiveness, ensure your tank is clean; accumulated debris in the filter will render the carbon ineffective.

Changing Activated Carbon

Activated carbon binds with contaminants and eventually becomes saturated, losing effectiveness. Replace it monthly for optimal results. Longer intervals won't harm the tank but will reduce effectiveness. If your water yellows or smells, it's time to replace the carbon.

Myth of Recharging Activated Carbon

Numerous myths claim activated carbon can be recharged through methods like baking it in an oven. These claims are false, as the temperature and pressure needed to recharge carbon are unattainable in a kitchen. It's best to purchase new carbon from a store and store unused carbon in an airtight container to prevent it from absorbing odors from the air.

De-Absorption

It's a common misconception that saturated activated carbon leaches adsorbed materials back into the water. This is inaccurate; de-adsorption requires water chemistry changes that don't occur in aquariums.

However, the processes used to create some activated carbon can result in the presence of phosphate in the end product. In this case, it is possible for phosphate already present in the activated carbon to leach into the aquarium water. Some activated carbon products will specifically state if they are phosphate-free.

If you struggle with high phosphate levels and cannot identify the cause, remove the activated carbon. Continue regular tank maintenance for several months to observe if phosphate levels persist. If they do, carbon likely isn't the cause.

Cautions With Carbon

While using activated carbon in your filter is beneficial, it's not essential. If you regularly test your water, perform partial changes, and dechlorinate tap water, carbon is optional. It becomes an ongoing expense due to monthly replacement.

The carbon in a recirculating filter system will also act as a home to the beneficial bacteria that turn ammonia into nitrite and then nitrate. When you change the carbon each month, you are throwing away part of the biofilter, and it will take a while for the new carbon to grow beneficial bacteria on it. If the carbon media is a significant percentage of your filtration system, you will be losing your biofilter with each replacement. An ammonia spike could possibly occur after adding the new carbon. To prevent this from happening, use sponges, beads, bioballs, or ceramic beads in sufficient quantity in the filter to act as the main media for bacteria that form the biofilter.

Powdered activated carbon can disperse as fine dust in the aquarium, settling on fish gills and causing harm. Cases have been reported where improper containment in media bags led to fish fatalities, with carbon particles found in gills and fins. To prevent this, use larger pelleted or granular carbon, and rinse it with distilled water to remove dust before placing it in the filter. Rinsing with distilled or deionized water also prevents the carbon from adsorbing chlorine from tap water.