Using Activated Carbon In Aquarium Filters – Beginners Guide

Activated carbon is used in aquariums to filter the medium and make it favorable for water-living organisms. But the debate on using activated carbon in aquarium filters has been muddled over time because of different beliefs! Activated carbon is considered standard media by some while others believe it is not enough to fulfill the living requirements of aquatic species.

Using activated carbon is highly beneficial for aquatic organisms as it purifies water bodies effectively, but it can be worse if you’re not taking care of quality and quantity. Precisely, it is imperative to use carbon content in the right proportions! To settle down these opinions and queries, I did extensive research and used carbon in the aquarium to see what happened!

Using Activated Carbon In Aquarium Filters

Using Activated Carbon In Aquarium Filters

Introduction To Activated Carbon

Activated carbon is a porous material with a chemically attractive nature. It can appeal to the organic chemicals and carry them within. As far as activated carbon for fish tanks is concerned, the first carbonaceous material used for the medium was “char”. Char is a chemically treated no-oxygen substance interconnection capability that allows it to attract and carry organic chemicals present in a medium.

Activated carbon has been confused with activated charcoal by a lot of people as they think both are different things! For your information, carbon has many synonyms including char, charcoal, and more. All these terminologies are interchangeable with each other. In a word, there is no difference between activated charcoal, activated char, and activated carbon in the field of carbon filtration.

When we indulge in the chemistry of aquarium charcoal, we see two different processes that are absorption and adsorption. Absorption refers to the phenomenon in which an absorbent material like a sponge soaks up the liquid, while the adsorption is related to the molecular, ionic, and atomic attraction over the surface of an adsorbent. The question here is whether the activated aquarium carbon absorbs the chemicals or absorbs them?

In a word, the activated charcoal follows “ADSORPTION—a surface process”! Activated carbon provides a porous and chemically attractive surface area where organic compounds, impurities, or unwanted particles stick. The material providing the porous surface, for example, activated carbon is called adsorbent, while the chemicals that come to stick to this surface are known as adsorbate. This phenomenon can be explained using a tabletop or any glass surface!

When we place an activated carbon in the medium where there are many unwanted organic chemicals present, a special attractive force exerts on these organic molecules, ions, or atoms. Due to this force, the molecules change their direction towards the adsorbent in an imbalanced manner. The adsorbent keeps holding the molecules over its surface until the medium reaches the “EQUILIBRIUM” stage. It refers to the balance of adsorbent and adsorbate means activated carbon has no left space for new entries.

When all the entries or pores over the surface of activated carbon are fulfilled, the adsorption process automatically stops. It is an indication that you should change the substrate adsorbent to continue the procedure. That’s all for adsorption, but what does activated carbon do in aquariums, or using activated carbon in aquarium filters is good or bad? Let’s move on to the detailed context of carbon for aquariums!

Activated Carbon For Aquariums


Using activated carbon in aquarium filters has benefits, but there is a controversy in this debate! Activated carbon is primarily used to reduce the chemical concentration to make water healthier and more favorable for aquatic life. These hazardous chemicals are added to the aquariums to treat fishes from bacterial or fungal infections, but once their application is done, there is an urgent need to remove them.

But some people think that activated carbon has no special role as you can also change the old water with new to reduce the concentration of those chemical agents. New water would be completely safe and effective for the better growth of aquatic organisms. With the flip of a coin, some people think that old water is healthier or better for fishes than new water, as according to their opinion, aquatic species become used to their habitat and once you change it their survival becomes challenging.

When you don’t change the water, it becomes yellowish or brownish with time and also produces an unpleasant pungent odor, which not only causes a risk to the lives of your pets but also becomes intolerable for pet owners. To get rid of this disgusting situation, people used to put activated carbon in tanks as it reduces the coloration of water and absorbs all the toxic chemicals.

The idea of better old water is pretty old-school, and after tons of research, people become aware that freshwater is more beneficial for aquatic life. Now, we usually change half-tank water once or twice a week to make sure that their pets are growing in a healthier and safer habitat. So, you see, all the beliefs and concepts collide together and leave us with a question: do I need carbon in my aquarium filter?

Activated carbon is used as a filtration medium in aquariums primarily to remove unwanted chemicals through the adsorption process. The aquariums become smelly due to lack of aeration which is not only unhealthy for fish but also makes the outside of the tank unhygienic and unpleasant. The addition of activated charcoal into such a medium removes the pungent odors.

Secondly, carbon filter fish tanks maintain the actual color of the water as activated char removes the food colors including red, green, yellow, or brown, from the water. These colors are usually released from low-quality fish food. For your information, cheap food not only leads to medium coloration but also is unhealthy for aquatic organisms, so pet owners should take care of that!

People use some decorative stuff to make the aquarium look prettier. In this sequence, decorative wood is used often to enhance the overall appearance of the tank and make it look like a natural habitat. However, these woods release tannins in the medium, which are bitter astringent compounds with acidic nature. Tannins are toxic for living organisms, but there is no need to worry about them when you are using activated carbon in aquarium filters because carbon adsorbs these poisonous compounds.

Furthermore, the aquarium medium has been treated with various anti-bacterial, anti-parasitic, or antifungal agents that keep the environment healthy and safe for aquatic organisms. However, the overdose of these agents increases the concentration of some chemicals like malachite green, methylene blue, or more, which indirectly cause hazards to fish. Using activated carbon in aquarium filters removes these chemical dyes effectively and makes the waterbody healthier and more pleasant!

In a nutshell, using activated carbon in aquarium filters is an effective way to remove toxic chemicals from the medium and make the habitat more favorable for aquatic organisms. But regardless of all those benefits explained above, there are some drawbacks of using activated carbon in aquarium filters too. Carbon and its compounds have a considerable concentration of phosphates in them, and higher phosphate levels promote the growth of algae which is life-threatening for fishes!

Now that you are aware of both the good and bad sides of using activated carbon in aquarium filters, it’s time to decide what you think is best for your pets! Once you decide to opt for aquarium carbon filters, there are some considerable factors you need to address. For instance, the quality and quantity of activated carbon! I’ll describe them all shortly so make sure to give a good read:

Activated Carbon Quality & Quantity

The activated carbon is available in the market in both cheap and good qualities: a low-quality carbon tends to promote algae growth enormously as it contains a high number of phosphates. In contrast, a good quality carbon is the one with promising adsorptive properties and lesser phosphate content; however, it costs you more bucks! Spending a bit more sounds like a reliable idea here, otherwise, you’ll put your pets in danger.

The word “activated” is very significant here as a deactivated carbon is of no use! What does carbon do in a fish tank? Adsorbs the unwanted content and purifies the water by reducing the coloration, pungent smell, toxic chemicals, and more! Activated carbon provides a surface that is open for adsorption and makes water clearer and healthier, while deactivated carbon can do nothing like that!

In simple words, I would say you should opt for a quality activated carbon that follows adsorption excellently. But how can you determine or measure the quality of carbon? The quality of a carbon element is measured by its molasses number, ash concentration, and iodine count. Activated carbon with 1000 iodine count and 225 molasses number is considered a quality one. Another way to look at carbon’s quality is via its surface area.

As I said before, adsorption is a surface phenomenon in which the toxicants attract towards the surface and bind to it. In other words, we can say activated carbon holds the pollutants. The following surface trend is followed here: a large surface area opens more sites for holding unwanted chemicals and simultaneously promotes the effective adsorption/cleaning/purification and vice versa.

The surface of carbon consists of pores: macropores (which are large) and micropores (which are small). Macropores make bonding with big molecules while micro-ones are compatible with tiny pollutants. The quality carbon is the one that consists of both macro and micropores so that it holds all kinds of pollutants big or small, and cleans water effectively.

Now that you know what quality carbon is, we move on to the “QUANTITY” of activated carbon for fish tanks! The activated carbon aquariums should contain no more than two cups of carbon content for up to fifty-five gallons of water (2: 55). There is no such hard and fast rule that means you can change the ratio a bit based on the quality of activated carbon you’re using or the volume of the tank but make sure to not increase the quantity adversely.


How do you use activated carbon in aquariums?

How to use or add the activated carbon in aquariums is among the most asked questions after what does carbon do for a fish tank! The aquariums have some free slots where you can place a bag of activated carbon easily. These mesh bags are easily available in all fish stores and will cost you no more than five dollars only. Fill the mesh bag with activated carbon and place it in the slot and you’re done!

Does activated carbon affect pH in aquariums?

Using activated carbon is among the popular techniques for water purification. Like other filtration techniques, the pH spikes become more visible or prominent in carbon-treated water. In a few words, “YES” the activated carbon affects the water pH.

Can you use too much-activated carbon in aquariums?

Using activated carbon is beneficial as long as you’re not over-dosing it! Carbon contains phosphates which promote the growth of algae in the water. Some species of algae form poisonous compounds which can put the fishes or other aquatic life in danger. It is also revealed that algae depletes the oxygen content and indirectly kills the aerobic organisms. In short, over-using activated carbon in filters leads to dangerous consequences.


Activated carbon brings a bunch of benefits and purifies water bodies effectively. It reduces water coloration, unpleasant odor, toxic chemicals, and unwanted or organic substances from water without putting the life of aquatic organisms in danger. However, carbon contains phosphorus which leads to algae outbreaks that lead to oxygen depletion and the release of poisonous chemicals. Therefore, you should be aware of the quantity, quality, and usability of activated carbon for pet fishes like a pro petter!

Leave a Comment