What is Aquarium Carbon and Its Benefits for Water Quality

Carbon is a key element used in aquarium filters to remove chemicals and keep the water safe for both freshwater and saltwater fish. Common materials for carbon filters include charcoal, coconut shells, and wood. These materials contain a lot of elemental carbon. When treated with high-pressure steam, these materials release impurities and form activated carbon with many tiny pores. Activated carbon acts like a sponge, effectively removing organic chemicals. It has millions of pores, giving it a large surface area - up to 750 square feet per ounce (69.7 square meters per 28.3 grams). This makes activated carbon very absorbent and useful for filtering aquarium water, as well as drinking water and odors in the air.

Three-Step Process:

• Carbon attracts negatively charged chemicals because it has a positive charge. This pulls the chemicals into the tiny pores of the activated carbon. This process also causes bacteria to settle on the carbon surfaces.
• Once in the carbon, the toxic chemicals are neutralized. Bacteria that break down ammonia and nitrite convert them into a less harmful chemical called nitrate. Small amounts of nitrate are safe for the fish and other aquatic life in the aquarium.
• Chemo-absorption is the process where chemicals are tightly bound to the carbon. The carbon pulls dissolved chemicals out of the water and holds them so they do not dissolve back in. When the activated carbon is removed from the filter, the chemicals are taken out with it.

While activated carbon removes dissolved wastes from the water, the organic waste that remains can still decompose and release more ammonia. This process increases nitrate levels in the aquarium, which must be reduced through regular water changes. That’s why it’s crucial to replace the activated carbon in the aquarium filtration system regularly. Additionally, performing water changes to remove some of the chemical wastes can reduce the strain on your carbon filter. This helps the carbon last longer before it needs to be replaced.

The Quality of Carbon:

Good quality activated carbon is measured by the iodine number, molasses number and the ash content. [algone.com/activated_carbon.php; available on 08/08/2008 22:00 CET]

• The iodine number of activated carbon shows its porosity. A higher iodine number means the carbon is more porous, with more tiny holes for absorbing chemicals.
• The Molasses number measures the carbon's ability to absorb larger chemical molecules. A higher Molasses number indicates better performance in capturing these larger substances.
• pH level in the aquarium water. This can be harmful to fish. Too much ash will reduce the effectiveness of the activated carbon.

When looking for good quality activated carbon, it's crucial to check the labels carefully. A reputable company will clearly list important details like ash content, density, phosphate levels, and porosity. If a company doesn't provide these details, their carbon might not be very effective. High-quality aquarium carbon will have more pores compared to lower-quality options. It usually comes in round granules rather than irregular shapes. This helps prevent the granules from packing too tightly, allowing water to flow more easily through the filter. Smaller granules are better at absorbing because they offer more surface area per volume. Top-quality carbon is also acid-washed to reduce ash and phosphate content, typically using hydrochloric or sulfuric acid in the process.

The Effect of Carbon on Water Quality:

The main reason for using an activated carbon filter in an aquarium is to improve water quality. Ideally, it should have a positive effect, but that’s not always guaranteed. Activated carbon with too much ash or phosphates can actually harm the water quality and be detrimental to the fish and other creatures living in the tank.

If activated carbon has too much ash, it can quickly raise the water’s pH. During the activation process, carbon is exposed to very high heat, which produces ash as a by-product. Since activated carbon is organic, it naturally contains phosphates. Some brands use acid washing to reduce ash and phosphates, but this process can’t completely remove them. However, it helps prevent harmful levels of these substances from leaching into the water. Soaking the carbon in water for a few days before use can further reduce leaching without affecting its effectiveness. Phosphate removers, available at aquarium stores, can help control phosphate levels. High phosphate levels can promote algae growth, so it’s important to keep them in check to limit algae. These removers are safe for both fresh and saltwater aquariums and do not change the pH. Activated carbon can also remove tannic acid from the water, which might come from driftwood or bog wood. Tannic acid, or tannins, doesn’t harm fish but can make the water appear yellowish-brown, giving the aquarium a dirty look.

One question a lot of people go through when owning an aquarium is: Do I really need active carbon filtration in my aquarium? The answer is really up to the aquarist because there are pros and cons to both sides.

Not having an activated carbon filter may lead to a buildup of bad smells and harmful chemicals in the aquarium water. More frequent water changes will be required in order to keep up the quality of the water. A filtration device for debris should still be used to extract floating waste from the water which should still be aerated for oxygenating purposes. So is it a good idea not to utilize activated carbon in the aquarium? Some people feel strongly against the use of activated carbon due to the amounts of phosphate it can bring to the water which will inevitably lead to cloudy water and algae growth. Activated carbon will also raise the pH in the aquarium to a certain degree depending on the ash content and quality of the active carbon.

Regardless of all the negatives to having activated carbon in the aquarium, there are a number of benefits that just might be worth it. Firstly, the quality of carbon purchased for use in the aquarium has a lot to do with how well it works. An acid washed brand will have less ash and phosphate which eliminates a large portion of the problem. Phosphate removers and pH testing can help to further handle the chemistry of the water. Although frequent partial water changes still have to be made, it will not have to be done as often if say there was no activated carbon filtration. Bad smells in the aquarium water will be eliminated due to the carbon and many of the organic wastes will be removed once the old carbon is extracted to be replaced by new carbon.

Questions and Answers

These questions were added on March 19, 2011, as part of merging aqua-fish.net/answers with our articles. While some may be answered elsewhere on this page, we’ve included them here for easy access. If you don’t find the answer to your aquarium carbon-related question here, please use the form at the bottom of this page to ask us. All questions listed below were submitted by visitors to aqua-fish.net.

• Which aquarium carbons contain phosphates?

  Answer: All aquarium carbons contain some level of phosphates. Lower-quality brands tend to release more phosphates into the water than higher-quality ones. To determine which brands are better, place a sample of the activated carbon in a bucket of water and test the phosphate levels. This will help you choose the right brand. Phosphate removers can also be used in your aquarium to control phosphate levels without affecting the water’s pH, which helps prevent algal blooms.

• Should the foam or carbon be placed first in the Tetra Whisper Filter?

  Answer: The foam, or bacteria sponge, should be placed before the carbon filter in the Tetra Whisper Filter. This setup ensures that chemicals and debris are removed from the water by the foam before it reaches the carbon filter. The nitrifying bacteria in the foam will then process the ammonia and nitrites. Finally, the cleaned water is returned to the aquarium.

• Why should you remove carbon from the filter when adding medication to the tank?

  Answer: Carbon in the filter will absorb the medication, preventing it from treating the water effectively. Removing the carbon ensures that the medication remains in the water and can work on the fish as intended.

• Why should I replace the carbon in my filter regularly?

  Answer: Carbon in the filter removes toxins and helps keep the tank clear. Over time, the carbon becomes saturated and can start releasing toxins back into the water. Regularly replacing the carbon ensures it continues to effectively clean the water and prevents it from reintroducing pollutants.

• Why is carbon used in an aquarium?

  Answer: Carbon is used in an aquarium to remove discolorations and clear up any residual medications after treatment. It helps keep the water clean and clear for a healthier environment for your fish.