Many different materials are offered, especially for external filters, which should enable perfect filtering of the aquarium water. There are also significant price differences between similar or almost identical materials.
Different material types
- filter floss
- blue filter sponge
- granules
- Ceramic or sintered glass
With filter floss, the smallest threads can come loose. Allegedly, these threads can wind around the axis of the filter pump or get into the aquarium. There should be indications that fish can die on the threads of the filter floss that have been eaten. However, concrete first-hand experiences are not known.
Foam materials, such as blue filter sponge, do not dissolve. Damage to the sponge can only occur if it is used for a very long time or if it is washed out too much.
Different filter materials such as broken lava, substrates, e.g. B. Ehfi substrate, or zeolites.
Artificial materials are made of ceramic or sintered glass. Due to the manufacturing process, these materials always have a similar structure.
Some simple theory
In principle, the filter material should provide as much surface area as possible. Bacteria settle on this surface and break down pollutants in the water. Therefore, porous materials are preferred. These offer colonization space for the bacteria not only on the outer surface. Due to the porosity, these materials are traversed by many small channels, which also have surfaces for the bacteria. The smaller and finer the pores are, the more pores can be accommodated and the more surface is created.
Many manufacturers therefore outdo each other with information on how much surface area their filter material offers.
On the other hand, pores that are too small quickly become clogged with sludge, filter sludge, etc., so that the filter material can no longer be flown through. The filter needs to be cleaned more frequently.
The necessary surface does not necessarily have to be provided directly by the filter material. If mulm can form in the filter, the mulm offers a lot of surface area for bacteria. According to this principle z. B. filter floss and partly also filter foam.
When buying the filter material, not only the largest possible surface is important.
Biological filtration
Whether biological filtration takes place in a filter at all is discussed again and again.
Filters do not filter biologically
- In relation to the amount of water, the amount of filter is only small.
- The high flow rate in most filters washes many bacteria out of the filter.
- Due to the high flow rate of the water, the bacteria do not have enough time to absorb food from the water.
Filters filter biologically
- The filter materials create low-flow zones in the filter so that there is sufficient biological filtration.
Anaerobic filtration
When water slowly passes through a filter, anaerobic, ie low-oxygen, zones can form. Bacteria can settle there and use the oxygen in the nitrate for their metabolism. These bacteria convert nitrate into oxygen and nitrogen.
In principle, anaerobic areas can form in any filter. It is debatable whether anaerobic areas form in external filters.
Anaerobic zones can form in external filters
- With slow flow and good filter material, anaerobic areas form.
Anaerobic zones cannot form in external filters
- External filters are always flown through too quickly, so that anaerobic areas can never form. Therefore the selection of the filter media has no influence on the formation of anaerobic zones in external filters.
- Water coming out of the filter contains practically the same amount of oxygen as the aquarium water. The water in the filter is therefore not low in oxygen or much less oxygen.
- Anaerobic zones only develop in special nitrate filters.
Practice
In practice, there are zealous advocates and just as zealous opponents for every filter material. While many aquarists recommend blue filter sponge and filter floss as the only filter materials, other aquarists criticize that these materials clog up too quickly and therefore have to be washed out too often.
Some aquarists doubt the filter effect of tubes made of ceramic or sintered glass because no sludge etc. has settled after a few months of operation, others report that a lot of sludge has settled in the same tubes.
There are no systematic and well-founded studies from which clear conclusions can be drawn. These are too complex for private aquarists. Reproducible tests would have to be repeated several times, bacteria counted, etc. Individual examples and individual measurements do not allow any meaningful conclusions.
What is certain is that no expensive materials are necessary. Blue filter sponge and filter floss are sufficient. That’s why more expensive materials like Siporax don’t have to be worse. However, there are also no known clear advantages.
Filters with foam
Filter foam Photo: Norbert Heidbüchel
Aquarium foam must be used. Normal foam has closed pores for thermal insulation. With aquarium foam, the pores are torn open with ultrasound.
Blue filter sponge is mostly used. There are commercially available sheets of blue filter sponge that can be cut to fit any filter as needed.
Most manufacturers already offer suitable filter sponges for their filters. However, this is usually significantly more expensive than the plates.
- Coarse foam is used in lower layers.
- Fine foam is used for upper layers.
- The top layer consists of filter floss.
This filter construction provides a large surface area and is inexpensive. As a rule, the water flows from the bottom to the top in external filters. If there is only a weak flow through a filter constructed in this way, it can be regarded as a special form of mat filter.
If there are several baskets in a filter, a suitable filter structure can look like this:
- Lower basket: coarse filter sponge, fine filter sponge, filter floss
- Upper basket: coarse filter sponge, fine filter sponge, filter floss
After every three months, the lower basket is placed on top. The upper basket is restocked and inserted below. A basket is then always retracted. Whether the top basket in each case can become so clogged that even anaerobic degradation processes take place is again dependent on various boundary conditions, e.g. B. Frequency of filter changes, flow, pollution, water changes, etc.