Advantages and disadvantages of external filters in the aquarium
Advantages external filter
- There are also suitable external filters for very large aquariums.
- Can be hidden in the base cabinet.
- If the substrate needs cleaning, there is a water splashing area just in the bathroom.
Disadvantages external filter
- Consume more electricity than internal filters because the water lines are longer.
- In the event of leaks, e.g. B. bursting of the hoses, water runs out.
- Regular cleaning is more complex than with internal filters.
- Small fish that can no longer get back into the aquarium can get into the filter through the coarse-meshed intake baskets.
The advantages and disadvantages listed are primarily intended to provide clues as to what should be considered when making a purchase.
Most of the disadvantages of the respective filter type can usually be prevented or at least mitigated by certain measures.
Splashing around in the aquarium can be prevented with modern filters if they have the appropriate devices for changing the filter material.
Hose clamps prevent e.g. B. the bursting of the hoses in external filters.
As with external filters, the flow rate can be reduced
After cleaning, external filters usually have a significantly higher flow rate for a few weeks than before cleaning. The reason for this is that the smallest particles clog the filter material over time.
As a result, the current in the aquarium can 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 becomes clogged, the wider the shut-off valve is opened.
Modern filters sometimes have a built-in shut-off valve to regulate the flow rate.
A shut-off valve can also be retrofitted to the filter circuit. 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 vacuum from the pump can release gases from the water, which could destroy the pump.
So the hose that runs back into the aquarium is throttled. Some filters make a rattling running noise after throttling or become a little louder.
It is more elegant to install a bypass between the pressure and suction side. A shut-off valve is placed in this bypass. When the tap is closed, all the water runs through the aquarium. The flow in the aquarium is large. If the shut-off valve is opened, the throughput in the aquarium is reduced and the flow is lower because part of the water flows through the bypass.
The throughput in the filter remains the same. So there are no running noises and the filter cannot be damaged for other reasons.
Throttling does not reduce power consumption, it can even increase slightly. When buying a filter, you should therefore not choose too high a performance. In the case of external filters, a distinction is made between pump capacity and flow rate. Depending on the filter medium and service life, the flow is approx. 4/5 of the pump output or even less. A fundamental problem is that because of the biological effectiveness, an external filter with a large volume makes sense, but it should have a relatively low flow rate.
However, the manufacturers always install pumps with immense flow rates in external filters of a corresponding size.
How to prevent the aquarium from leaking with external filters
With external filters there is a risk that a hose will come loose and then all 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 gaff 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 water surface, only air is sucked in and no more water runs out. Smaller holes clog too quickly. For example, if the hole B. is placed five centimeters below the water surface, a maximum of five centimeters of water can leak out. Of course, the filter or the pump can then run dry.
If the hole is placed too high, it may interfere with water changes. In the example, only five centimeters of water can be changed.
Of course, the hole can be so far below the water surface that water can be changed without any problems. Then, in the event of a malfunction, not too much water should run out before the hole is reached. In large tanks, the required amount of replacement water is often greater than the tolerable outflow volume.
In such cases, the filter must be turned off during the water change. It is often discussed whether bacteria die during this time. Experience has shown that a filter can be switched off for several hours or even days without any problems occurring when it is switched on again.
Alternatively, the hole can be closed with a plug during the water change. However, there is a risk of forgetting to remove the plug after changing the water. The protection is then of course ineffective.
Where external filters have to be
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 from Eheim should e.g. B. 0.5 to 1.20 meters below the upper edge of the water level. The water must practically fall into the filter. Only then is the relatively low flow rate or pressure head of the filter pump sufficient.
If an external filter is placed above the aquarium or at the same height, the filter performance drops sharply, many air bubbles form in the filter and starting up after cleaning is problematic.