External filters in the aquarium

external filters

All you need to know about external filters for your aquarium before you get one

Now that you have made up your mind on an aquarium, you need to figure out which filter you need. Some people opt to go with an external filter.

Find out more about external filters below.

Advantages and disadvantages of external filters in the aquarium

Advantages of external filters

  • There are also suitable external filters for very large aquariums.
  • Can be hidden in the base cabinet.
  • If the substrate needs cleaning, there is only a splash of water in the bathroom.

Disadvantages external filter

  • Consume more electricity than internal filters because the water pipes are longer.
  • In the event of leaks, e.g. B. Chipping of the hoses, water leaks.
  • Regular cleaning is more time-consuming than with internal filters.
  • Large-meshed suction baskets allow small fish to get into the filter, which cannot be returned to the aquarium.

The advantages and disadvantages listed are primarily intended to give you an idea of ​​what to look for when buying.

Most of the disadvantages of the respective filter type can usually be prevented or at least alleviated by taking certain measures.

Splashing in the aquarium can be prevented with modern filters if they have the appropriate devices for changing the filter material.

For example, hose clamps prevent flaking of the hoses in external filters.

Aquarium Filters External Vs Internal What’s Better

Can the flow velocity of external filters be reduced?

After cleaning, external filters usually have a significantly higher flow rate for a few weeks than before they were cleaned. The reason for this is that the smallest particles clog the filter material over time.

This can cause the current in the aquarium to be too strong after cleaning the filter.

The flow rate can be regulated with an interposed shut-off valve. After cleaning, the stopcock is closed slightly so that the flow in the aquarium is reduced. The more the filter clogs, the wider the shut-off valve is opened.

Modern filters have partially built-in a stopcock to regulate the flow rate.

A shut-off valve can also be built into the filter circuit at a later date. The tap must be used on the pressure side of the filter pump. I.e. the tap goes into the hose that pumps the water from the filter pump into the aquarium.

If the hose in front of the pump is throttled, the resulting negative pressure of the pump can release gases from the water that could destroy the pump.

So the hose that runs back into the aquarium is throttled. Some filters make a clattering noise or become a little louder after throttling.

It is more elegant to install a bypass between the pressure and suction side. A stopcock is placed in this bypass. If the tap is closed, all the water runs through the aquarium. The flow in the aquarium is great. If the shut-off valve is opened, the flow in the aquarium becomes smaller and the current less, because part of the water flows through the bypass.

The throughput in the filter remains the same. So there is no running noise and the filter cannot be damaged for other reasons.

The power consumption is not reduced by throttling, it can even increase slightly. When buying a filter, you should therefore not choose too much power. In the case of external filters, a distinction is made between pump performance and flow. 

Depending on the filter medium and the service life, the flow rate is approx. 4/5 of the pump output or even less. A fundamental problem here is that an external filter with a large volume makes sense because of its biological effectiveness, but which should have a relatively low flow rate.

The manufacturers always install pumps with immense pumping capacities in external filters of a corresponding size.

external filters
External filters for your aquarium

How can I prevent leakage when using external filters in the aquarium?

With external filters, there is a risk that a hose will come loose and then all of the aquarium water will run out.

Modern external filters usually have connections with which the hoses are clamped and can hardly slip off. Older external filters can be secured with hose clamps and possibly gaffer tape. The water runs out very slowly through the gaffer tape.

A 2 to 3 millimeter hole is drilled into the inlet pipe under the water surface. When the water level has dropped so far that the hole is above the surface of the water, only air is sucked in and no more water runs out. Smaller holes clog up too quickly. If the hole is placed five centimeters below the water surface, a maximum of five centimeters of water can leak. Of course, the filter or the pump can then run dry.

If the hole is placed too high up, it may interfere with the water change. In the example, only five centimeters of water can be changed.

The hole can of course be so far below the water surface that water can be changed without any problems. Then, in the event of a fault, not too much water should leak out until the hole is reached. In the case of large pools, the required amount of replacement water is often greater than the tolerable flow rate.

In such cases, the filter must be switched off during the water change. It is often discussed whether bacteria die during this time. Experience has shown, however, that a filter can be switched off for several hours or even days without any problems when it is switched on again.

Alternatively, the hole can be closed with a plug while the water is being changed. However, there is a risk of forgetting to remove the plug after changing the water. The protection is then of course ineffective.

Where should I place the external filters?

External filters must always be lower than the aquarium. The filters do not have self-priming pumps, but normal centrifugal pumps.

The filters only work when they are under the aquarium. Filters should be 0.5 to 1.20 meters below the top of the water level. The water must practically fall into the filter. Only then is the relatively low delivery rate or pressure head of the filter pump sufficient.

If an external filter is above the aquarium or at the same height, the filter performance drops sharply, many air bubbles form in the filter and tarnishing after cleaning is problematic.

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