The external filter - practical, powerful, space-saving

By external filter we mean a filter that is located outside the aquarium. In the aquarium itself, we have in this case only the water inlet, through which the filter sucks the aquarium water for cleaning, and the water outlet, through which the cleaned water returns to the aquarium. This is a great advantage, especially for display aquariums and aquascapes - firstly, it gives you much more scope for beautiful aquarium design, and secondly, no ugly filter housing spoils the great look of an artistically designed layout. Thirdly, an appropriately sized external filter also increases the total water volume of the aquarium - and the more water, the more likely pollutants can be buffered.

The filter inlet on most filters is not safe for juvenile fish or for small offspring of dwarf shrimp. It can be mitigated by either putting it inside a cut piece of fine filter sponge or by using a replacement cartridge for an airlift filter. Not so good is a cover made of fine tights. The fine fabric clogs up much too quickly and then makes the filter tight. Better here is really a correspondingly fine filter sponge.

Here in this store category you will find two types of external filters: once the classic external filter or canister filter, which consists of a water inlet, a water outlet and a filter pot connected to these devices with hoses, in which there are various filter materials for fine and coarse filtration. Thanks to the length of the filter hoses, the filter pot can be easily hidden in the aquarium base cabinet and thus does not get in the way.

Inside the filter housing of an external filter, there is space for filter media such as filter mats, filter fleece and filter tubes. Dizzyingly high numbers of filter bacteria settle on the surfaces of the filter material in the filter bowl. In the course of nitrification, they oxidize ammonium to nitrite here and then oxidize the nitrite further to the comparatively harmless nitrate. To do this, the filter bacteria need oxygen, which the filter inlet supplies together with the water. Sometimes even a denitrification takes place, during which bacteria dissolve the oxygen out of the nitrate (NO3). What remains is atmospheric nitrogen gas, which is absolutely harmless for our aquarium inhabitants. For denitrification, the water must be absolutely free of oxygen so that the bacteria are "forced" to crack the oxygen out of the nitrate.

You can also buy backpack filters here. They also have the great advantage that they are not in the aquarium and thus can not take up space. Backpack filters are especially recommended for smaller aquariums. They do not take up space in the base cabinet, and if you want to take a nice picture of the set up aquarium or aquascape, you can simply remove the backpack filter, take the picture and then hang it back on the tank. The backpack filter also contains filter materials. Even with the backpack filter, the filter inlet should be defused with a piece of filter sponge or a replacement cartridge for airlift filters to prevent juvenile fish, small snails or baby shrimp from entering. They would be cut to pieces by the filter wheel, which is something an aquarist wants to avoid at all costs!