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Aquarium Fish Tank Filtration


Aquarium / Fish Tank / Turtle Tank Filtration

How it all works

Water filtration at the best of times can be confusing for a new comer and it can also be very complicated for even the very experienced. Because of this we have written this article explaining in an easy to understand format, how it all works.  Most people believe that a filter is only there to keep the tank clean, and remove free floating debris. Although this is one aspect of what a filter does, there is a much more important thing that a filter is used for.

There are three types of water filtration.

1. Mechanical Filtration

This filtration of water is done by passing the water through a screen, or a thin piece of sponge, or through some filter wool, all of which remove pieces of debris from the water.

2. Chemical filtration

This filtration is done by passing the water through small pieces of specialised filter media. The most common ones are Carbon, Purigen, Zeolite and Bio Chem Zorb. We recommend all aquatic animals have some Purigen and or Bio Chem Zorb in the filter.

3.  Biological filtration

This filtration is the most important and is done best having a filter which not only has foam or wool in it, but also has some ceramic noodles, bio balls or some other kind of bacteria attracting media.

This biological filtration is the key to growing "good" bacteria in your tank to break down pollution and keep your tank water nice and healthy for your inhabitants. Initially in a new tank there is no good bacteria, and it can take 2-8 weeks for it to grow. We call this period "cycling" of your new tank.

The most common ways to cycle a tank is to add some cheap fish which will provide the neccessary pollution for the good bacteria (nitrifying bacteria) to feed off. The other way is to slowly stock you tank while adding products like Stabilty or Cycle to help speed up the growth of the good bacteria.

Aquarium Fish Tank Filtration

In a new tank Ammonia (NH3) usually spikes in the first two weeks until bacteria grows to break it down. Once Ammonia is all gone there is a secondary spike of Nitrite (NO2) which again needs more good bacteria to break this down. Once there is no Ammonia or Nitrite present we say our tank is "cycled" which means our tank is now running nicely with enough good bacteria to deal with the pollution (Ammonia and Nitrite). We still need to be careful not to put too much pollution into the tank (i.e livestock and food) at any one time so our bacteria population can grow at the same rate as our increasing pollution level. In a tank with the correct size filter, livestock population, feeding regime, and regular partial water changes, your tank should never get Ammonia or Nitrite again.

Now that our tank is all running smoothly and we have no Ammonia and Nitrite we will now start to get some Nitrates (NO3). This is what our filter has turned our Ammomnia and Nitrites into. When kept at low levels this is harmless to our tanks inhabitants. Regular partial water changes and the use of Purigen and or Bio Chem Zorb will help to keep Nitrates at an acceptable level.

Although we refer that the "tank" that is now cycled it is really the filter that has gone through the main process, as this is where most of our good bacteria will be.

Types of filters:

Internal Sponge Filters

These filters are one of the most popular but unfortunately it is due to their low cost and not because of their high performance. Sponge filters rely on the sponge for both mechanical and biological filtration and with only a small area on the sponge for bacterial growth they are really only suitable for smaller tanks and are very rarely recommended by us unless when filtering very small amounts of water.

Internal Sponge/Media Filters

These are a much better option than just plain sponge filter as the also have a section for adding filter medium like noodles. This enables a much larger surface area for good bacteria growth without relying solely on the sponge for all aspects of filtration. The Fluval U2, U3 and U4 have this media compartment as well as the Hailea RP 600. These are suitable for 25 litres up to around 200 litres depending on what is being kept in the tank.

Under gravel Filters

Under gravel Filters are one of the oldest kinds of filtration and are still popular with some even today. Although quite good as a biological filter as they pull water through the gravel creating a good surface area for bacteria they have many flaws. The main problems are they do not have a mechanical aspect to them which means they just pull all the waste to the bottom of the tank. The other is that if your turtles or fish expose any of the under-gravel plate, water will pass through that section rather than through the gravel which in turn will stop the biological aspect of the filter.

Hang On Filters

These filters can be quite effective as they can accommodate all 3 areas of filtration. They will only work reliably in a tank that is full of water so they are not suitable for turtles. They are generally designed for tanks that are under 100 litres. Keep in mind that these filters trickle water back into the tank so they will be a bit noisier than others.

Canister Filters

These filters are generally the most preferred due to the ability to put plenty of filter media in them. There are a wide range available on the market to suit all sizes of tanks. Always check to see what type of and how much media they come with as some may appear cheap due to having no media in them which basically makes them a sponge filter. Always check with us to see what size is suitable for your tank, but turning the water over at least 3 times per hour is usually recommended.

Sump / Trickle Filters

One of the best filters for biological, mechanical and chemical filtration. The reason they are so effective is they are not limited by the amount of oxygen in the water as the media has the water trickling through it rather than being submersed in water. Air is 20% oxygen so the surface of the filter media is oxygen rich allowing for maximum bacteria growth compared to water which can only hold 7%. There is plenty of room for sponges and chemical filtration pouches. There are many different designs to suit different uses so feel free to discuss this with us. Generally used on larger tanks, marine tanks, or for use with multiple tank systems.

UVC Filtration

UVC (Ultra Violet Clarification) filtration can be used as an additional filter with all of the above. Please note these are NOT a biological filter and will not work like the above filters to break down Ammonia and Nitrite. UVC filters are mainly used for controlling suspended algae (green water) in fish tanks and ponds and can help improve a fish's chance of fighting bacterial diseases and parasites. Using a UVC filter will not affect the beneficial bacteria in your biological filter. Globes must be changed at least every 12 months.

Hints and Tips

  • Don't over clean your filter. Every time you clean your filter you will be killing some bacteria so don't clean it just for the sake of it.
  • ALWAYS use discarded tank water when cleaning any filter material. Never wash under the tap as the cold water and chlorine will kill good bacteria.
  • When upgrading to a new filter always let the old one run for at least 4 weeks. Alternatively take the filter media material from the old filter and put into the new one as this will have the good bacteria.
  • Always ask when buying a new filter. Don't just presume that because it says it is suitable for 200 litres that it will be suitable!
  • Don't overstock your tank and increase your stock levels gradually.
  • Buy yourself a complete water test kit so you can check your system regularly to ensure all water parameters are all ok.
  • Click to work out your fish tank water volume