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Fish Tank Filters & Their Purpose


Fish tank filters are definitely right up there in terms of importance. A well managed filter will set the ground work for a stable and successful aquarium. As for what is the best aquarium filter, that will depend largely on the type and size of aquarium you have.

The reasoning behind using aquarium filters is pretty straight forward. It is used to keep the water clean and safe for fish to live in. This will include dirt that you can see and the dirt that you canít see.

Dirt that you can see will include excess food that your fish donít eat. Even if you are very careful there will more than likely be some food left over. This fish themselves also secrete visible waste and there will also be some waste from plants in your tank.

Dirt that you canít see includes chemicals or toxins that are released from the fish and from decaying food and plant waste. Some chemicals are even in the water you use to fill your tank up with.

Now with all that in mind we can move onto how the filters manage to remove these wastes. There are 3 ways that a filter will work to remove waste from your fish tank. Most fish tank filters will use all 3 of these methods, but some filters will only use 2 methods.


These methods are:

1. Mechanical Filtration

2. Biological Filtration

3. Chemical Filtration


Now let me give you a quick breakdown on what each method is.

Mechanical Filtration


Mechanical filtration is what we referred to earlier about removing the waste in the aquarium that you can see floating about. Particles floating in the tank are easily visible, especially with the lights on. Clear water will make your aquarium look far more presentable when you have colourful tropical fish.

A fish tank filter will do this by sucking the dirty water from the tank and passing it through some filter material before pumping it back into the tank.

The filter material (media) used could be anything from foam or sponge, filter pads, gravel or a combination of media types. The smaller the holes are that the water needs to pass through, the more waste the filter will be able to trap.

The type of filter media that you use will depend on your requirements. One point to remember is that media with very fine holes in it will get blocked up very quickly and need to be changed often. Media with big holes may not remove enough of the waste from the water.

Choose your media to suite your needs; unfortunately the best way to do this is by trial and error until you find the correct balance.

Biological Filtration


Bio filtration is probably the most important filtration method in any aquarium. An interesting fact to note about bio filtration is that it doesnít only happen inside your fish tank filter, but on all surfaces inside your fish tank.

It is called biological filtration because it is brought about by live bacteria in the tank which remove waste from the water. These bacteria can live inside filters and any other surface in an aquarium.

Now people often associate the word bacteria with bad things, but it this case they are doing good work. Read more about these very important bacteria in our page on the Nitrogen Cycle.

These bacteria flourish inside your filter because the water passing through it is always brining in fresh toxins which the bacteria need to survive. Live plants in your aquarium also help the fish tank filter to remove toxins from the water.

A by-product or left-over toxin from biological filtration by bacteria is Nitrate. This Nitrate is removed manually from the water by doing regular small water changes. You should only change 10% to 15% of your water at a time to avoid shock to the fish. Again, if you want to know more about this then check out the page on the Nitrogen Cycle.

Chemical Filtration


Chemical filtration involves the use of solid materials that are placed into the fish tank filter to draw chemicals out of the water. The solid media that is normally used is a type of charcoal, otherwise known as Activated Carbon.

Activated carbon filter media is able to draw chemicals out of the water. A downfall of carbon is that it has a short life span and needs to be changed regularly. You will probably have heard about some of the dangers of activated carbon.

If the Carbon you use is not changed when it is saturated or full, then it is likely to do the opposite of clean your water. Once the carbon is full, instead of capturing chemicals it starts releasing chemicals back into the water. Some of these chemicals that are released back into the water are potentially more dangerous than when they were absorbed.

Some people prefer to use some of the carbon replacement resins that are available on the market. These resins can perform the same function, but some are only designed for certain chemicals.

The main bit of advice here is to read the manufacturers label on any of these products before you buy them. This way you can be sure that it will perform the job you want it to and you will be aware of how to use it properly.

Tip: Multiple Fish Tank Filters


The importance of backup systems comes to light everyday in real life business and production operations. Your fish tank is no different, but having two filters has more of an advantage than just being a backup if one of them fails.

Your aquarium filters should be slightly over-sized in comparison to your fish tank. This way you can increase the time between having to clean them out.

Come time for cleaning, you will be able to either clean them 1 at a time, or clean half of each filter.

Cleaning both filters out at the same time would break the Nitrogen Cycle and the possibility is there that you could end up with a lot of dead fish.

You never want to clean all of your filters because they house all the good bacteria that are needed to remove toxins from the water.



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