Gtstricky, Reef Aquarium New Sump, marked as public domain, details on Wikimedia Commons
An aquarium problem
The film layer on the water surface of an aquarium
In many aquariums it forms over time a greyish, milky or oily layer on the water surface. This film throws streaks in the surface flow if the layer is thick enough. These streaks can also contain gas-filled bubbles.
This film often produces a dazzling play of colors reminiscent of oil contamination in a puddle of water. In aquaristics this is often referred to as significant aesthetic impairment felt.
The biological impairment of the aquarium by the surface film
Aside from its unsightly nature, the surface film of an aquarium deserves attention primarily because its accumulation interferes with vital gas exchange at the air-water interface.
In addition, this film impedes the light transmission of the medium by shading, thereby impairing oxygen production and the growth of aquatic plants. Overall there is one Lowering the total oxygen content of the pool.
Even in heavily planted tanks, plants only produce oxygen during the light window, which is around 8 to 12 hours in most tanks. However, organisms such as fish, bacteria and other microbes consume oxygen throughout the day.
And plants also consume oxygen in the dark. This means that most of the time an aquarium relies on surface gas exchange to produce oxygen.
Good oxygen levels are crucial for an active bacterial colony that will help break down organic waste. This activity of microorganisms, in turn, keeps algae in check.
The following applies: The seemingly harmless surface film of an aquarium can lead to a variety of problems.
The scum as a biofilm in the aquarium
The surface film of the aquarium is mostly a microbial biofilm. This biofilm consisting of bacteria and other microorganisms is called scum skin.
Causes of the formation of the surface film
How scum forms in the aquarium
Five main causes can be identified for the formation of scum. To overview:
- Excess organic waste
- Change in plant growth factors
- Inadequate oxygen circulation
- excess of iron
- Stress conditions by tending the aquatic plants
Excess organic waste
Organic waste is often not consumed by the filter quickly enough, both in newly set up aquariums that are not yet biologically mature and in tanks with a filter that is too small.
As a result, these accumulate on the surface. A good level of oxygen is present here, which supports a thriving microbial colony that feeds on this excess waste.
In the aquarium, the surface film is usually formed by the plants releasing proteins as they adapt to a new environment.
The plant material released by the necessary regeneration then accumulates on the water surface of the aquarium. This often takes the form of an oily film.
Change in plant growth factors
These changes can be triggered, for example, by new lighting conditions, a new fertilizer or new equipment.
As plants gear up to adapt to the new tank conditions, they release proteins that deposit on the surface, often as an oily film.
Interestingly, improving the biological basin conditions can lead to a temporary increase in the surface biofilm.
Inadequate oxygen circulation
In a biologically unstable tank with already insufficient oxygen circulation and the resulting poor gas exchange, the microbes prefer to stay at the water surface where there is plenty of oxygen.
This is a vicious cycle as the accumulated surface film reduces gas exchange even further.
excess of iron
In some aquariums, excessive iron fertilization leads to a viscous white film in which bacteria feed on the iron that is then abundant.
Stress conditions by tending the aquatic plants
Many tanks with a lot of light and high potential for increasing plant mass growth speed, which are exposed to weekly plant care, plant pruning and replanting, are often in a state of constant stress and thus cause the formation of a scum layer by the release of plant material.
This will occur even with a seasoned cymbal that otherwise has no other problems.
Ways of treating scum in the aquarium
The simplest option is a mechanical one: use a surface skimmer over the water inlet of the filter. This directs the water surface biofilm into the filter where it is broken down and greatly improves the gas exchange potential of the aquarium.
On a more fundamental level, scum is not inevitable. Well-established tanks with slow and stable plant growth usually have no surface film.
And this even without the use of a skimmer or the presence of strong mechanical surface movement. The conditions mentioned for the formation of mold skin do not occur here.
What is a skimmer?
The skimmer as «scoop»
Basically, a skimmer is a Device for removing floating contaminants on a water surface.
The process of «skimming» (from English skim – skimming) thus represents in principle a technology for waste water treatment with physical means.
skimmer technique
working principle
According to the principle of action, two types of skimmers can be distinguished:
- adhesion skimmer
- overflow skimmer
The adhesion skimmer
The adhesion skimmer works according to the adhesion principle. The components to be removed are removed by adhesion to a medium.
A typical example of this would be a belt skimmer, which uses a belt drawn through the liquid medium to remove oil. The oil collects preferentially on the skimmer material and can be pumped out. Water does not stick to the skimmer and drips off.
The overflow skimmer
The overflow skimmer follows the principle of gravity (“hole in the water” principle). It essentially consists of a receiving part and the floating body.
The cleaning performance depends on the throughput and the layer thickness of the medium to be removed.
The skimmer in the aquarium
Technique of the aquarium skimmer
Adhesion skimmers as well as overflow skimmers can be used in the aquarium. These three forms of skimmer technology are used in aquaristics:
The protein skimmer
A protein skimmer is a device used to remove organic compounds from water. It is used not only in commercial applications such as municipal water treatment plants, but also for home filtration primarily in marine aquariums.
Protein skimmers are an essential element of water treatment in saltwater aquariums. They remove suspended matter and sediment from the water before it can settle on the bottom of the aquarium.
The protein skimmers are available in a variety of sizes, shapes and price ranges. There are two main types of skimmers:
- internal skimmer
- external skimmer
Internal skimmers are located inside the aquarium. Because they mount to the inside of the aquarium, they are easy to install and maintain.
External skimmers are installed outside of the aquarium, either as a freestanding unit next to the aquarium or as an installation in a sump or sump.
Due to their dimensions, external skimmers offer higher performance, but are more complex to install and maintain. As a rule, due to the compact design, an internal skimmer for seawater aquariums with a capacity of up to about 100 liters is recommended.
For larger volumes, the use of an external skimmer should be considered. Skimmers are also rarely used in freshwater aquaristics.
The overflow chamber
The use of an overflow chamber is also often considered in seawater aquariums. In this case, the surface water is routed over an overflow comb and fed into the filter circuit.
As an internal filter with an overflow comb and floor drain, this principle of surface cleaning is occasionally also used in freshwater aquaristics.
The water is only sucked off the surface if the flow through the filter comb is sufficient.
The surface suction
Apart from the physical principle on which it is based, surface extraction is essentially nothing more than a skimmer. is nothing more than a surface skimmer. And while the intake strainer of the external filter is usually installed quite deep, the inlet of the skimmer is located directly on the water surface.
The inlet of the skimmer can either be adjusted to match the height of your water level. Or it is equipped with a float.
In this way, the surface suction can independently adapt to a changing water level, which has arisen, for example, due to evaporation.
The surface suction is therefore a small overflow in the aquarium into which the surface water drains directly. Water from deeper layers is still sucked in. The amount of water that is absorbed on the surface, however, is not sufficient for most external filters.
When should a skimmer be used in the aquarium?
A skimmer is recommended to be used in an aquarium if a biotope with soft water is to be reproduced and as little technology as possible is used.
Because with a skimmer that is integrated into the filter circuit, you improve the gas exchange on the surface. This increases the CO2 and oxygen content. As the CO2 level increases, so does the pH. Many fish like this and unless you are keeping very demanding plants you may even be able to do without a compressed gas system altogether.
A skimmer can also help you if you have problems with a film of water from time to time. In the case of acute problems, however, you should first use one that has a separate water circuit.
However, you should not use a skimmer if you want hard water. The skimmer increases the CO2 content and thus lowers the pH value, but in this case…