Aeration is a common practice in aquariums, where compressors or filter-pumps are used to supply oxygen and aerate the water. However, there are certain issues and principles related to this process that need to be considered.
Aeration, derived from the Greek word “aer” meaning air, involves artificially saturating various media with air to oxidize the organic matter they contain. Oxygenating the deeper layers of water is achieved through the mixing of water masses, including water circulation and other factors.
In an aquarium, a minimum of 5 mg/l of oxygen is required to meet the breathing needs of fish. If the oxygen level falls below this threshold, fish can suffocate. However, simply meeting this minimum requirement is not sufficient to ensure the proper functioning of the aquarium’s biological system. The goal of aeration is to achieve the optimal level of oxygenation. Adequate oxygenation is crucial for not only fish and microorganisms to breathe but also for reducing the concentration of pollutants and harmful substances in the aquarium.
Hemoglobin serves as the major transporter of oxygen in fish blood. In most fish species, the absence of gas exchange practically eliminates the presence of hemoglobin. Fish living in oxygen-rich environments, like those in our aquariums, can only bind oxygen when it is available in significant amounts. Research on certain fish species has shown that increasing oxygen levels in the water significantly improves overall fish health, appetite, disease resistance, growth, weight, sexual function in adult fish, food digestibility, metabolism, and blood composition.
Several factors influence oxygenation in aquariums. Temperature plays a significant role as it affects various physical, chemical, biochemical, and biological processes in the aquarium. Higher temperatures reduce water’s saturation with oxygen. For example, a temperature range of 24-27 degrees Celsius is suitable for cichlid fish. Temperatures above this range, especially for extended periods, are not advisable. Many tropical aquarium inhabitants thrive within this temperature range. Thermometers and thermostats are used to measure and maintain the desired temperature.
Microbubble aeration is another method worth considering. It involves passing air through a perforated diaphragm or a finely porous diffuser to oxygenate the water. This technique is commonly used in installations for deep biological water purification, where microorganism activity is most intense. Bubble size significantly affects water oxygenation. Smaller bubbles result in better oxygen transfer. Tests have shown that using small bubbles with a diameter of around 0.1 mm can enrich water with approximately 10 grams of oxygen per cubic meter of air at a diving depth of 1 meter. In contrast, aeration with larger bubbles (2 mm in size) reduces oxygen enrichment by half. Rising air bubbles continuously carry water to the surface, aiding oxygenation.
It’s important to note that aeration aims to enrich water with oxygen, but it should not be confused with oxygenation. Air only contains 21% oxygen. For instance, if a compressor blows air into a tank at a rate of 300 l/h, only 60 l/h of oxygen is delivered. This fact does not lead to an oxygen deficiency in the tank.
In densely populated rearing tanks with a high number of fish, it’s crucial to have powerful air supply systems, such as compressors or active air pumps, alongside water filtration. These systems ensure sufficient oxygen supply due to the abundance of organic matter, food particles, and fish waste. In such tanks, a larger quantity of food is provided to promote fish growth. However, it’s essential to promptly remove any uneaten food and feces to prevent oxygen depletion caused by organic matter decomposition.
While ornamental aquariums may not have as significant an organic content issue as densely populated tanks, organic matter can still accumulate in the substrate and pre-filter compartments. Organic deposits are often visible on the edges of internal filters and similar systems. Regular cleaning of the filter cavity is necessary to prevent excessive organic build-up.
Many hobbyists use “closed” external filters, which primarily function as mechanical filters. These filters cannot actively supply water with oxygen. In these setups, it becomes crucial to aerate the water intensively. This is because the oxidation of organic matter accumulated in the filter requires a substantial amount of oxygen. Aeration becomes necessary not only for the normal respiration of aquatic organisms but also to compensate for the oxygen consumed during the oxidation process.
To conclude, it’s essential not to overlook systems that enrich aquarium water with oxygen. If compressor noise is a concern, modern devices or equipping the “output” hose with a filter can be considered. It’s also helpful to have tests for measuring oxygen content in the water and collect measurements throughout the day. These tests will provide valuable insights and answers to many questions related to aquarium oxygenation.