Clarifying activated carbon for filter – filtration media for aquarium, pond and aquaponics

EHFI Karbon 5L – Eheim activated carbon bag for external aquarium and aquaponics filter

EHEIM Karbon activated carbon for aquarium filters

Name: EHEIM Karbon activated carbon for aquarium filters
Brand: EHEIM
SKU: H2501051
Price: 12.0 USD
Availability: InStock

$12.00

This EHEIM activated carbon fills the last stage of the filter, after the mechanical and biological stages, and binds whatever colours the water, gives it an odour, the chlorine from the mains and medication residues. It stays active for about 4 weeks before it needs replacing, and is sold in 1, 2 or 5 litres, with or without a net bag.

Ref. H2501051·Filter media

Format : 1 liter

1 Liter

1 Liter (+Net)

2 Liters (+Net)

5 Liters

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The summary

What you receive: loose activated carbon, with its retaining net on two of the four versions.
How long it works: about 4 weeks, after which it needs replacing.
Where it goes: last, after the mechanical media and after the biological media.
When to remove it: before each treatment, and fresh carbon goes in once the course is finished.

The final stage of the filter, which removes what the other media let through

EHEIM Karbon activated carbon fills the last stage of the aquarium filter, after the mechanical and biological media. By adsorption, it retains whatever colours the water, its odours, mains chlorine and medication residues. It works for about 4 weeks before it needs replacing, and is sold in 1, 2 or 5 litres, with or without a net bag.

Activated carbon retains by adsorption, at the surface of its pores, molecules that are already dissolved in the water: whatever tints it yellow, whatever gives it a smell, the chlorine supplied by the mains and the residues of medication. A foam or a ceramic stops particles, whereas carbon acts on what no mesh can catch. It is therefore placed last in your filter, after the mechanical and after the biological stages, and its lifespan is counted in weeks, since it becomes saturated as it binds these molecules.

📅 A treatment lasting about 4 weeks

After about 4 weeks, the pores of the carbon are full and it no longer binds anything. The molecules it was holding are only adsorbed on its surface, so they can come loose after a while: exhausted carbon left in the filter stops being useful, then releases some of what it had retained. Because exhausted carbon looks exactly the same as new carbon, write the date it was installed on a piece of tape stuck to the filter or set a reminder on your phone, and replace it when it is due.

💊 Carbon and treatments

Because it binds medication residues, it also binds the medication you have just added. So remove the bag before starting any course of treatment, whatever it is, and put in a fresh one once the treatment is finished: it then removes whatever is left of the product from the water. The relevant treatments can be found in the fish care section, to be chosen once the problem has been identified. During treatment, the filter keeps running and the nitrifying bacteria stay in place in the other media, since only the carbon bag is taken out.

Fill the first two stages of the filter

Carbon comes at the end of the line, and it stays effective for longer when the earlier stages of your filter trap the particles and house the bacteria. Pick up at the same time what you need to fill the first mechanical stage and the bacterial media. In a complete filter, the carbon receives water that has already been cleared of its particles, so its pores remain available for dissolved molecules instead of clogging with dirt.

🧺 Choosing the size and the bag

The volume you plan on should match the free space in your filter's basket, once the mechanical and biological media are in place. The 1 litre size fills most domestic aquarium filters, and the mesh bag version stops the granules from spreading through the basket, which also makes them easier to remove before a treatment. Replacing it every 4 weeks, the 5 litre bucket gives you 5 refills of a 1 litre basket, or around 5 months of continuous use. Rinse the granules in clean water before use, until the water running off is no longer black with dust. In an aquaponics system it is used in the same way, occasionally, as it also holds back some of the dissolved elements intended for the plants.

Technical specifications

The essentials

What it holds in place: Colour, odours, chlorine, medicationAlso traces of cleaning products, pesticides and dyes.
Duration of action: About 4 weeksOnce this time has passed, it no longer binds anything and may release some of what it has retained.
Place in the filter: Last, after the biological stageIf fitted earlier, it becomes saturated with particles instead of molecules.
Medium: FreshwaterDesigned for freshwater tanks and circuits.

To budget for separately

Retaining net: On the versions without a netLoose carbon scatters in a filter basket without its bag.
The previous stages: Mechanical and biological mediaCarbon works as a finishing step, never on its own.

In the box

1 pack of loose activated carbon, 1, 2 or 5 litres depending on the version
1 retaining net on the versions that mention it

Manufacturer's values recorded on 20/09/2026. The duration of action is an order of magnitude given for moderately loaded water.

Manufacturer and product safety

Manufacturer: EHEIM GmbH & Co. KG
Postal address: Plochinger Str. 54, 73779 Deizisau, Allemagne
Contact: info@eheim.com
Website: eheim.com

Information provided under Regulation (EU) 2023/988 on general product safety.

Which filter media is missing from your filter?

Three media sold in the same volumes, which are not placed at the same stage or for the same reason.

Three media, three stages, three maintenance routines The first stops what can be seen, the second houses the bacteria, the third removes what remains dissolved.

	Filter stage	What it treats	Bacterial colony carrier	Acts on colour and odour	Routine maintenance	Replace after	To be removed during treatment	Price
EHEIM MECH ceramic pre-filtration noodlesYour choice	First, at the water inlet	The larger particles	Yes	No	Rinse it, tap water is fine	Never	No	$13.00
EHEIM SUBSTRATpro biological filtrationYour choice	Second, after the mechanical stage	It houses the bacteria	Yes	No	Rinse it in tank water	Never	No	$12.00
Recommended EHEIM Karbon activated carbon forYour choice	Last, after the biological stage	Dissolved molecules	No	Yes	Replaceable	4 weeks	Yes	$12.00

EHEIM MECH ceramic pre-filtration noodles

Space in the filter

Filter stageFirst, at the water inlet

What it treatsThe larger particles

What the media provides

Bacterial colony carrierYes

Acts on colour and odourNo

Maintenance

Routine maintenanceRinse it, tap water is fine

Replace afterNever

To be removed during treatmentNo

EHEIM SUBSTRATpro biological filtration

Space in the filter

Filter stageSecond, after the mechanical stage

What it treatsIt houses the bacteria

What the media provides

Bacterial colony carrierYes

Acts on colour and odourNo

Maintenance

Routine maintenanceRinse it in tank water

Replace afterNever

To be removed during treatmentNo

EHEIM Karbon activated carbon forRecommended

Space in the filter

Filter stageLast, after the biological stage

What it treatsDissolved molecules

What the media provides

Bacterial colony carrierNo

Acts on colour and odourYes

Maintenance

Routine maintenanceReplaceable

Replace after4 weeks

To be removed during treatmentYes

Manufacturer's values recorded on 20/09/2026.

Estimate your
delivery time

Lightweight parcel, dispatched within 48 hours by Colissimo or Chronopost to your home, as you choose at payment. The exact cost depends on the method selected.

Frequently asked questions

6 questions

6 key questions

Does it need to be removed during a treatment?

How long does it stay active?

What happens if I forget it in the filter?

Where exactly does it go in the filter?

Does it need to be used all the time?

No. It addresses a specific situation:

water that has turned yellow or has an odour;
the end of a treatment;
a new filling with mains chlorine.

Once the situation is resolved, the first two stages of the filter are enough. Using it continuously means replacing it every month, and in a planted tank it also removes the fertilisers you add. The article on cloudy water sets out the cases where it helps and those where it will make no difference.

Does carbon change the pH of the water?

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EHEIM Karbon activated carbon for aquarium filters

The summary