The tasks of the aquarium filter
© Mari_art stock.adobe.com ID: 163111141
Most aquarium filters are designed to ensure mechanical and biological filtration in the aquarium. With mechanical filtration, coarse particles are filtered out of the water by getting caught in the filter material as it flows through the filter. In most filters, the water first flows through a layer of filter floss, which carries out the mechanical cleaning, in which the coarse particles get caught.
Biological filtration is even more important for the health of the fish than mechanical filtration. The biological filtration does not take place directly through the filter materials. The filter should provide as large an area as possible on which as many filter bacteria as possible can settle. These filter bacteria convert pollutants (faeces, uneaten food, etc.) dissolved in the aquarium water into harmless substances. The filter is filled with porous material such as foam, small clay rolls, filter floss, etc. so that a large area for settlement is available.
Apart from special cases and special filters, all filters should perform these two tasks, regardless of whether they are internal or external filters and what filter material the filters are filled with.
Why the aquarium filter should be cleaned as seldom as possible
The longer the beneficial bacteria can multiply undisturbed, the more bacteria are in the aquarium filter. The more bacteria there are in the filter, the greater the biological degradation capacity of the filter, ie the faster pollutants can be broken down, or the more pollutants can be broken down. After about 6 months, a community of bacteria, fungi and other microorganisms has formed in a filter, which ensures maximum biological filtration. During this time, the so-called filter sludge forms in the filter, which is not dirt but the desired “filter mass”. A good filter culture smells pleasantly of soil or compost heaps and does not stink. Basically, biological filtration is also a type of composting.
When cleaning the filter, however, many of the existing bacteria and other living beings are washed out again and again. After cleaning, the filter performance is impaired until the living beings in the filter have multiplied to such an extent that the full filter performance is available.
Show all internal filters* Show all external filters*
The influence of flow velocity
If the water flows through the aquarium filter very quickly, the bacteria have difficulty settling in the filter because they are carried away by the water. Fast-flowing filters therefore usually work mainly as mechanical filters. Since zones in which the water flows more slowly are also formed there due to increasing pollution over time, biological filtration also takes place, but this is not as effective as in filters with a slow flow. In principle, these so-called quick filters only act as a sieve.
In filters with slowly flowing water, the bacteria can stay better in the filter material. In addition, the polluted water stays in contact with the bacteria longer, so that overall better biological filtration takes place.
How often the aquarium filter is cleaned
The filter becomes clogged over time due to the coarse dirt particles that get caught in the aquarium filter and the filter sludge. The water flow decreases until finally hardly any water flows through the filter.
According to another rule of thumb, the filter is cleaned when only 50% of the aquarium contents flow through the filter in one hour. To measure this, you time the time it takes for one liter of water to flow out of the filter into a measuring cup or bucket. The time and amount measured is extrapolated to one hour and compared with the contents of the aquarium.
Only then should the entire filter material be cleaned.
If there are already too many coarse particles in the water before this point, the material responsible for mechanical filtration, usually filter floss, is cleaned or replaced first. In filters with separate mechanical and biological filtration, the material responsible for mechanical filtration can be cleaned or replaced weekly if necessary. The materials responsible for biological filtration are cleaned as seldom as possible.
The time until the next cleaning depends on many factors such as aquarium size, filter size, fish stock, feeding, plant growth, etc. As a guide, it can be assumed that the usual small filters in small aquariums up to approx. 120 liters must be cleaned every four to six weeks. Larger filters in large aquariums need to be cleaned about every 6 months, but can last a year or more.
Fast flow filters with mainly mechanical filtration are cleaned more frequently. Frequently cleaned quick filters permanently remove unwanted organic substances from the aquarium, while biological filtration converts them. Depending on the aquarium, this can have advantages, but also disadvantages. For example, the nitrate produced can again be useful as a fertilizer for the plants. If there is otherwise too little nitrate, it is desirable for the plants to remain in the aquarium. On the other hand, if there is too much nitrate in the aquarium overall, this can lead to increased growth of algae.
How to clean the aquarium filter
The cleaning of the filter material takes place in water that has approximately the aquarium temperature. Lukewarm water is also suitable. If the water is too cold or too hot, too many filter bacteria can die off. It is ideal if you use aquarium water for cleaning. Since the creatures in the filter are used to this water, very few filter bacteria die off.
The cleaning is not carried out in the aquarium, after all the substances are supposed to be removed from the aquarium. The old water from the aquarium that was sucked out when the water was changed is well suited.
Filter floss, filter foam and similar material are easily squeezed out, clay rolls etc. are carefully rinsed out or cleaned by stirring in water. The material is roughly cleaned until significantly less «brown broth» comes out of the filter material, but not until only clear water comes out of the filter material. The «brown broth» contains the important bacteria as a starter culture for recolonizing the filter material.
Before inserting the cleaned filter material, the filter housing is thoroughly washed out. The turbine wheel is cleaned and freed from plant residues etc. that have wrapped around the axle. Depending on the filter, the pump housing can also be dismantled and cleaned.
Water change and filter cleaning at the same time
It is often not recommended to clean the aquarium filter at the same time as changing the water. However, there are only relatively few of the filter bacteria in the open water.
These mainly settle in the filter, in the sludge, in the substrate or on surfaces. Normally, therefore, only very few of these bacteria are removed from the aquarium with the water change. The effect is probably hardly measurable or noticeable compared to filter cleaning. At best, if a lot of existing mulm is sucked off at the same time, there may be so much missing bacterial mass that the aquarium becomes unstable. In a stably running aquarium, simultaneous water changes with moderate suction of sludge and filter cleaning should not be a problem.
Show all internal filters* Show all external filters*
Filter substrate does not usually have to be changed.
The filter substrate (filter material) mainly serves as a settlement area for bacteria that break down the pollutants contained in the water. Porous material is particularly suitable for this purpose, as it provides a particularly large surface area due to its structure. Only part of the filter, usually the filter floss, is used for mechanical cleaning.
If a filter becomes clogged over time and only lets a little water through, it is first cleaned. The filter floss can usually only be cleaned a few times. If it has frayed into individual parts due to repeated cleaning, it is replaced with new filter floss. The remaining filter material is more resistant and can usually be cleaned many times. Only when the material is shredded or does not let enough water through even after cleaning, is it replaced with new material.
Sealing rubbers are lubricated with silicone grease once a year.