The black Activated Carbon pellets in the filter

The black Activated Carbon pellets in the filter

Postby orb-it » Thu Nov 26, 2015 3:14 pm

Over the years members have asked about the black pellets located under the Biorb filter sponge, often asking what they are and the task they perform. Below are a few pointers that will hopefully be useful explaining the basics of what the pellets are and the job they do

What is activated carbon.
Activated carbon is made up from organic based materials, some examples could be wood, peat, coal, even coconut shells, although not all are recommended for aquarium use.

To Activate the organic material it goes through a extreme heat process, reaching far greater controlled temperatures than our domestic ovens could ever reach, this increases its internal surface area and gets rid of impurities. Some sources mention being able to recharge carbon in the domestic oven but other sources seem to indicate it is only possible at controlled extreme temperatures in the range of 2,000°F.

Activated carbon works by both absorption and adsorption. Absorption is where pollutants are trapped in the pores of the carbon. Adsorption is the process where pollutants are chemically bonded to the sites and trapped by the activated carbon.

What does activated carbon remove
Activated carbon removes dissolved organic compounds, these are produced by many different processes in the aquarium such as tannins that can initially leech that tea stained colour from bog/aquarium woods. It will also remove some heavy metals and medication (for that reason activated carbon is always best removed from your aquarium filter before medicating the aquarium).

Activated carbon will also remove some phenols (which cause odours) this can be something like a break down in plants for example that can contribute towards a fishy smell. Activated carbon has also been said to remove some of the trace elements that are beneficial for plant growth.

What does activated carbon not remove
Activated carbon does not remove toxic ammonia, toxic nitrite or nitrate from water. There are also certain metals it will not remove such as Iron.

Can activated carbon alter PH
Aquarium activated carbon is often made from coal which tends to have a pH in the region of 8.5-10. Certain activated carbons can act as an ion exchange type media and adsorb carbon dioxide and that can contribute to pH increase. Rinsing or soaking the carbon before you put the carbon into the aquarium is said help with this issue. If you are using carbon 24/7 and you are experiencing a ph increase it may be beneficial to try a carbon free period for a few months to see if it is the cause. That being said some sources indicate if a the good quality branded carbon is sourced it could minimise or even eradicate this issue altogether.

Does activated carbon leech phosphates into the aquarium
Some activated carbons will leach varying amounts of phosphate into the aquarium water. This is because phosphate can sometimes be a naturally occurring part of the carbon or it can be from a chemical called phosphoric acid which is sometimes used in the activation process.

Phosphate can contribute to algae issues in the aquarium. However there are good quality coal based carbons available that are said to be phosphate-free or extremely low in Phosphates. For this reason it is advisable to use a high quality freshwater aquarium activated carbon, so buying something branded and checking its make up is recommended. If you suspect your activated carbon is contributing towards a elevated phosphate issue you could remove it entirely from your filter for a few months still performing your weekly maintenance with dechlorinated water changes then re-test your phosphate, if it remains the same it is more than likely not the cause.

Once the activated carbon is full
Activated carbon will become full in time as it binds with the compounds it removes so it is best replaced regularly. On the forum we recommend to replace the carbon every 4 - 5 weeks but if you are finding a buildup of detritus in your filter it would be beneficial to replace it more frequently. Some sources state that once the carbon has become full there is a possibility it can leech some of what it has removed back into the water, some indicate should you have a sudden change in water chemistry such as extreme shifts in PH it is possible for the carbon to dump back into the water some of the impurities it has removed. Ether way, for the brand of pellet you choose as there is no definite way of knowing that the carbon is full so replacing the carbon frequently will be advisable and help it to do the job it is added to the filter for effectively.

Where should activated carbon be placed in the filter

Due to its porous nature activated carbon will lose its effectiveness if exposed to a build up of detritus passing through the filter from the aquarium.

With this in mind it is better for the water flow in the filter to pass through the filter sponge before the activated carbon. That way the sponge will trap the detritus before it reaches the carbon. If this is not possible in the filter setup you are using replacing the carbon frequently should help this become less of a issue, the frequency will depend on the waste produced in your tank. If the activated carbon becomes covered in detritus it will no longer be effective.

Do you need to use activated carbon 24/7

Looking at the above there are definite advantages to using activated carbon in the filter.

It will remove good as well as bad from the aquarium and carbon should never replace frequent water changes. Weekly maintenance will help to keep the levels in check, replenish any lost nutrients and keep the water clear. It is advisable to have some pellets to hand however should you need to remove medications from the water after treatment for instance.

You may choose to run carbon 24/7, occasionally or only in emergencies, which ever method you choose you will soon find what works best for your aquarium.

This is just a snippet of information available on the biorbforum, for further tips, help and advice please click the register button located above. :D

BiOrb compatible sponges are available here:

10 Filter Pack – UKP £10 (inc. UK P&P)

10 Filter Pack – EURO €18 (inc. Europe EU P&P)

10 Filter Pack – USD $25 (inc. USA & rest of world P&P)

These filter sponges are fully supported on the biorbforum.
:nemo: BARGAIN BiOrb range compatible filter sponge replacements
:nemo: :nemo:
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