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What is aquarium carbon and it's advantages

Brief Description

This is a guide on using aquarium carbon with answers and FAQ. However you should also visit our second article too: Activated carbon - The purpose in a fish tank and we'd love to hear your experiences with aquarium carbon! If you'd like to ask a question that hasn't been answered in the article below, feel free to use a form at the bottom of this page and we'll answer!

Carbon is an element that is largely used in the aquarium industry for filtering chemicals out of the water making it safe for both fresh and salt water fish to live in. Materials such as charcoal, coconut shells and wood are often used for carbon filtering because of the amount of elemental carbon it contains. When these materials are introduced to high pressured steam impurities are released and the elemental carbon contained within creates pores. This forms the substance we call activated carbon which acts like a sponge that is highly effective against organic chemicals. Active carbon has millions of pores which gives it a substantially large surface area of up to 750 square feet per ounce. The tiny little pores make activated carbon a highly absorbent substance that is useful in filtering not only aquarium water, but it is also used to filter drinking water and absorbing bad smells in the air.

Three-Step Process:

  • The carbon attracts negatively charged chemical particles with its own positive charge. This draws the chemicals in causing it to enter the porous structure of the active carbon. This also causes bacteria to settle on the carbon surfaces.
  • Carbon will then neutralize the toxic chemicals that are present in the aquarium. The bacteria that are responsible for metabolizing the ammonia and nitrite will release it as a less harmful chemical known as nitrate. Nitrate can exist in the aquarium water in small amounts without harming the aquarium’s inhabitants.
  • Chemo-absorption is the process where chemical particles are tightly bound to the carbon. The dissolved chemicals are pulled out of solution form and held firmly by the carbon which inhibits it from re-dissolving back into the water again. When the activated carbon is removed from the aquarium filtration system, the chemicals are removed with it.

Even though the activated carbon will remove the dissolved wastes from solution, the organic wastes held tightly will still actively decompose releasing more ammonia into the aquarium water. This leads inevitably to the presence of more nitrates that need to be removed through water changes. That is the reason it is so important to constantly replace the activated carbon in the aquarium filtration system. On the other hand, actively changing the water to manually remove much of the chemical wastes will relieve some of the stress put upon your chemical filtration system. This will allow you to be able to utilize your active carbon for longer periods of time before it becomes inactive.

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 content of the activated carbon will be an indication of how porous it is. The higher the iodine number is, the more porous the active carbon will be.
  • The Molasses number indicates the carbons ability to absorb larger chemical molecules.
  • Ash is a product that results from activating the carbon containing materials. This inorganic substance will quickly and radically increase the pH of the aquarium water which can be harmful towards fish. An overabundance of ash will cause the activated carbon to be ineffective.

When searching for a quality carbon it is very important to read all the labels. An activated carbon company that has nothing to hide will clearly list all of the important details such as ash content, density, phosphate content and porosity. Some companies do not feel the need to specify the details of their activated carbon which means their carbon might be less than adequate. A high quality aquarium carbon will have much more pores in comparison to a low quality product. Aquarium carbon of a higher quality will consist of round granules as opposed to randomly shaped ones. This disables the carbon granules from packing too tightly, which allows the water to flow more smoothly through the carbon filtration. Smaller carbon granules are more effective in absorption because they will give you more surface area per volume than larger granules. High quality carbon will have been acid washed to reduce ash and phosphate content. Hydrochloric acid or sulfuric acid is generally used to complete the acid wash process.

The Effect of Carbon on Water Quality:

The whole purpose of putting an activated carbon filter in the aquarium is to affect the quality of the water. Ideally the water would be affected in a positive way but that is not always the case. Activated carbon that contains an overabundance of ash and phosphates can be detrimental to the quality of aquarium water and the lives of its inhabitants.

When the carbon contains too much ash it can rapidly increase the water’s pH. Carbon is subjected to very high heat in the activation process, and ash is one of the by-products. Since activated carbon is an organic substance it contains phosphates as all organic substances do. Some brands of activated carbon utilize an acid washing process to reduce the presence of ash and phosphates. Although the acid wash reduces the presence of ash and phosphate it cannot completely eliminate these substances. But at the very least, this process will prevent harmful amounts of chemicals from leaching into the water. It is recommended that the activated carbon be soaked in water for a couple of days prior to use. This step will help to prevent leaching into the water without lessening the effectiveness of the activated carbon. Phosphate removers are available in aquarium retail stores to help limit the presence of phosphates in the water. Algae grows well in phosphate so it is important to limit these levels in the aquarium in order to limit the amount of algae growth. Phosphate removers are non-toxic and can be used in both fresh and saltwater aquariums without altering the pH. Activated carbon will also filter tannic acid out of the water if they are present from any drift or bog wood decoration. Tannic acid is also referred to as tannins. Tannins are harmless toward fish but they do alter the color of the water leaving a yellowish-brown tinge which makes the aquarium look filthy.

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

The below-listed questions were added here on March 19th 2011 due to merging aqua-fish.net/answers with articles. While some questions may be partially answered above, they were added here "as is" because it's easy to find one that you're interested in this way. If you cannot find answer on your aquarium carbon - related question within this page, then use a form at the bottom of this page and we'll answer! All the questions below have been asked by visitors of aqua-fish.net.

  • Which aquarium carbon has phosphate?

    Answer: All aquarium carbons contain phosphate to some extent. The lower quality brands will tend to leach more phosphates into the water compared to some of the higher quality brands. Place a sample of some activated carbon in a bucket of water and test the water for phosphate content. After testing a few brands this way you may get an idea of which brands to use or not use. Phosphate removers can be used in the aquarium without altering the pH of the water. This will help prevent algal blooms from occurring.

  • Does the carbon or foam come first in the Tetra Whisper Filter?

    Answer: The foam, or bacteria sponge should be placed in front of the carbon filter. Chemicals and debris are filtered out of the water before the nitrifying bacteria metabolises the ammonia and nitrites. The filtered water is then spilled back into the aquarium.

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

    Answer: If the carbon is still in the filter it will soak up the medication and remove it from the water before it has worked on the fish.

  • Why do I need to replace carbon in my filter on a regular basis?

    Answer: Carbon is added to the filter to make the tank clear and free of certain toxins. After a period of time the carbon will become saturated and leach toxins back into the water. It should be replaced before this happens.

  • Why do we need carbon in the aquarium?

    Answer: Carbon is used short term for removing discolorations in the water or to remove any medications in the water after a course of treatment has finished.

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