A few words about filtration in the aquarium

Aquarium filtration

While setting up an aquarium, every aquarist firstly has to possess at least basic knowledge about the underwater environment maintenance. As many of you know, this is a complicated hobby and combining different aspects to create a balanced environment often needs a lot of articles to read. But that’s for one purpose: the final effect- a colorful tank full of dense plants and lots of beautiful fish. Today let’s get closer to a basic understanding of aquarium filtration.

Let’s start from the basis: filtration is a process of removing toxic substances from the aquarium. These toxic substances are mainly nitrates, nitrites and ammonia which is produced by plant leaves and with fish’ excrement, uneaten food or fish waste. The more of the inhabitants in the aquarium, the more of these toxic substances in the water. They can really endanger your aquarium’s life that’s why it’s very important to understand the filtration process.

Firstly, let’s divide the aquarium filtration process into three stages:

Phase 1- mechanical filtration

Phase 2- biological filtration

Phase 3- chemical filtration


If all of these types of filtration are being done well, the water should be crystal-clear :)


Mechanical filtration

Any material that can filter out debris or solid particles and doesn’t leach any substances will be good. Consider the flow rate of the pump as this will dictate how fast the mechanical filtration will work. Remember that mechanical filtration is not only about keeping your aquarium clean but also preventing the chemical and biological filter from being completely covered with declining matter. That’s why the mechanical filters should be put first where the water flows into the filter. The phase of mechanical filtration is very effective because it removes at least 75% of all the suspended solids before the water flows into phase 2- biological filtration. This means that the mechanical filter requires regular cleaning or replacing because that is the only one that is going to be ridden with gunk.


Biological filtration

There are certain types of nitrifying bacteria living in water that can convert ammonia to nitrites by eating them. Another type of beneficial bacteria eats Nitrites and converts it to Nitrate. This process is called the Nitrogen Cycle and if you haven’t heard about this phenomenon or if you want to deepen your knowledge click HERE.

Biological filtration is a medium that is a house for beneficial bacteria occurring in the Nitrogen Cycle. These types of beneficial bacteria need an oxygen source so they must be placed where water passes thoroughly (although this phenomenum happens everywhere in the tank). They will get oxygen from the passing water while ridding themselves of ammonia and nitrites. Remember that the medium of the biological filter on which the bacteria live must allow the water to flow freely through them, e.g. ceramics. Sufficient biological filtration is very important in every aquarium.

In newly setup aquariums it’s very important to let this phenomenoum “work” because it takes about 3 weeks or more for the bacteria to be balanced and properly functioning in the aquarium. If you’re setting up a new tank, again, please find our article about the Nitrogen Cycle, where we explained this matter in depth.


Chemical filtration

There are only two materials considered as perfect filter media: plants and activated carbon.

The most common substance that needs chemical filtration in the aquarium is the by-product of the Nitrogen Cycle- nitrate. Nitrate (Nitrogen) is one of the 3 macronutrients that our plants need. The point is to find the right amount of plants suitable for the aquarium. It can be achieved by performing the suitable aquarium tests, inter alia, to control ammonia levels in the water.

Activated charcoal is also a very good medium for chemical filtration. Placing it in the last chamber of the aquarium filter would be highly recommended for new aquariums. Disadvantage of this substance is that it has to be discarded within a few months. Find our article about activated carbon HERE to read more!

Other chemical filter media involve adding even more chemicals into the water to get rid of the unwanted toxic nitrogen compounds. This is a bad idea. There are too many unknown variables to risk using these products in the aquarium with live stocking.


The regular water change

The regular water change resets the aquarium parameters back to safe levels depending on how much is replaced. The safe water change is about 30-70% of the water. Replacing the whole aquarium water will disturb the water’s biology and in consequence get your fish shocked. The amount of the aquarium water that should be changed varies because different species have different requirements. Moreover, the tap water should be treaded if necessery. Learn how to do it weekly in the right way because this may decide whether your aquascape will be a successful attempt or a disaster aquarium!


The aquarium filtration system is definitely on the top of the list when we talk about basic knowledge every aquarium enthusiast should possess. Sufficient mechanical chemical and biological filtration is essencial for proper functioning of the aquarium. Understanding all types of filtration will surely help you to maintain a healty aquarium system and water clear in your home aquariums.