Cleaning aquarium filters: from A to Z

cleaning aquarium filters

Filter cleaning in the aquarium – frequency, necessity and implementation

Owning an aquarium comes with the responsibility of looking after the aquarium equipment. It is therefore important to learn everything you need to know about cleaning aquarium filters.

Cleaning Aquarium Filters: What purpose does the aquarium filter serve?

Most filters are intended to ensure mechanical and biological filtration in the aquarium. With mechanical filtering, 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.

Even more important for the health of the fish than mechanical filtering is biological filtering. The biological filtering 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 (excrement, leftover food, etc.) dissolved in the aquarium water into harmless substances. The filter is filled with porous material such as foam, clay rolls, filters floss, etc. so that there is plenty of settlement area available.

Apart from special cases and special filters, all filters should perform both of these tasks, regardless of whether they are internal or external filters and with which filter material the filters are filled.

Cleaning Aquarium Filters: Why should you clean the aquarium filter infrequently?

The longer the beneficial bacteria can multiply undisturbed, the more bacteria there are in the filter. The more bacteria there are in the filter, the greater the biodegradation capacity of the filter, i.e. 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, this is not dirt, but the desired “filter mass”. 

A good filter culture has a pleasant smell of soil or compost heaps and does not stink. Basically, biological filtering 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 organisms in the filter have reproduced so much that the full filter performance is available.

How To: EASILY clean an Aquarium Filter!

Cleaning Aquarium Filters: The influence of the flow rate

If the water flows through the filter very quickly, the bacteria have difficulty settling in the filter because they are carried away by the water. Filters with rapid flow therefore usually work mainly as mechanical filters. Since increasing pollution causes zones in which the water flows more slowly to form there, biological filtering also takes place, but this is not as effective as in slow-flowing filters. 

These so-called quick filters basically 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.

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Cleaning Aquarium Filters

Cleaning Aquarium Filters: How often should the aquarium filter be cleaned?

Due to the coarse dirt particles that get stuck in the filter and the filter sludge, the filter clogs over time. The water flow becomes less and less until finally hardly any water flows through the filter.

Only 50% of the aquarium contents flow through the filter in one hour should be cleaned. To measure this, stop the time in which one liter of water flows from the filter into a measuring cup or bucket. The measured time and amount is extrapolated to one hour and compared with the aquarium content. Only then should the entire filter material be cleaned.

If there are too many coarse particles in the water before this point in time, the material responsible for the mechanical filtering, usually filter floss, is cleaned or replaced first. In filters with separate mechanical and biological filtering, the material responsible for mechanical filtering can be cleaned or exchanged weekly if necessary. The materials responsible for biological filtration are cleaned as rarely as possible.

The time until the next cleaning accordingly 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 6 weeks. Larger filters in large aquariums have to be cleaned about every 6 months, but can also have a service life of a year or longer.

Fast-flowing filters with mainly mechanical filtration are cleaned more frequently. With frequently cleaned quick filters, unwanted organic substances are finally removed from the aquarium, while they are converted with biological filtration. Depending on the aquarium, this can have advantages, but also disadvantages. 

For example, the nitrate produced can again be used as fertilizer for the plants. If there are not enough nitrates otherwise, it is advisable to leave it in the aquarium for the plants to grow. On the other hand, if there is too much nitrate in the aquarium overall, this can lead to increased algae growth.

Cleaning Aquarium Filters: How to clean the aquarium filter

When cleaning aquarium filters, you have to remember that the filter material is cleaned in water that is approximately at the aquarium temperature. Lukewarm water is also suitable. If the water is too cold or too hot, too many filter bacteria can die. It is ideal to use aquarium water for cleaning.

Since the living beings in the filter are used to this water, very few filter bacteria die. The cleaning is not carried out in the aquarium; after all, the substances should be removed from the aquarium. Well suited is the old water from the aquarium, the water change was siphoned off.

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 so long until only clear water comes out of the filter material. The “brown broth” contains the important bacteria as a starting culture for the repopulation of the filter material.

Before inserting the cleaned filter material, the filter housing is washed out thoroughly. The turbine wheel is cleaned and freed of plant debris etc. that have wrapped around the axle. Depending on the filter, the pump housing can also be dismantled and cleaned.

Cleaning Aquarium Filters: Water change and filter cleaning at the same time

It is often not advisable to clean the filter at the same time as changing the water. However, there are only relatively few of the filter bacteria in free water. These settle mainly in the filter, in the sludge, in the ground or on surfaces. Normally only very few of these bacteria are removed from the aquarium with the water change.

Compared to filter cleaning, the effect is probably hardly measurable or noticeable. At most, if a lot of existing sludge is sucked off at the same time, so much bacteria may be missing that the aquarium becomes unstable. In a stable running aquarium, simultaneous water changes with moderate suction of sludge and filter cleaning should not be a problem.

Cleaning Aquarium Filters: Does the filter substrate need to be changed?

The filter substrate (filter material) mainly serves as a colonization area for bacteria that break down pollutants contained in the water. Particularly suitable for this is porous material which, due to its structure, provides a particularly large surface area. 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 is 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 tattered or when too little water lets through after cleaning is it replaced with new material.

Sealing rubbers should be greased with silicone grease once a year.