Introduction to Freshwater Fish
Setting up the tank
Filtration and aeration
An effective aquarium filtration system not only removes waste products from the water by physical or chemical means but also mirrors the process of biological filtration—the nitrogen cycle—that occurs in the wild. Filtration goes hand in hand with aeration, in which water is circulated so that it can absorb oxygen from the air and lose unwanted carbon dioxide.
In the confines of an aquarium, the waste produced by the fish can quickly build up to harmful levels without an effective filtration system. Filtration involves passing the water in the aquarium through one or several filtration media, which purify the water by biological, chemical, or mechanical means (see box, below). There are two basic methods of driving water through the media: using an electric pump, or relying on an airlift system, in which air bubbled into the tank through an airstone draws water up an airlift tube.
Undergravel filters—which are now used less commonly, compared with power filters—rely on a simple airlift system. A perforated corrugated or ridged plate is placed on the base of the tank and then covered by a substrate of gravel. The plate allows water to flow under the gravel, while the gravel particles— which should be at least 1 ⁄8 in (3 mm) in diameter to ensure good water movement—form the biological filter medium.
Power filters use an electric pump to drive water through the filtration media. There are two basic types: internal power filters, which sit inside the tank, and external filters, which are housed outside the aquarium and are generally used for larger aquariums. A range of different media are available for power filters: biological media, such as foam sponge and ceramic granules; mechanical media, such as filter wool; and chemical filtration media, such as carbon.
The most efficient filters use layers of different media in combination. It is often possible to add additional materials—for example, peat or coral sand—to this type of filter to alter the water chemistry. Efficient aeration is vital for the maintenance of a healthy tank, providing a source of oxygen not only for the fish but also for the beneficial bacteria within the biological filter. Using an air pump to pump air through an airstone (see p.41) can help to aerate the tank: the bubbles produced cause surface ripples that increase the area exposed to the air where oxygen exchange can take place. However, if there is enough surface movement generated by the outflow of the filtration system, an additional air pump may not be needed.
- Add zeolite sachets to remove ammonia from the water and a starter seed culture of bacteria for the biological filter.
- Be careful not to overfeed the fish and burden the filter with decomposing food.
- Test the water quality regularly to check the filter’s efficiency; frequent partial water changes (see pp.50-52) will ease the pressure on the filtration system
The nitrogen cycle is a natural process by which nitrogenous waste products are recycled. In biological filters in aquariums, growth of the bacteria that drive this cycle is encouraged.
- Fish in the aquarium eat plant protein, completing the cycle
- Ammonia is excreted by fish as waste and is also produced when any organic matter decays
- Beneficial bacteria present in the biological filter convert ammonia to nitrites
- Nitrites are converted to nitrates by other beneficial bacteria in the biological filter
- Plants absorb nitrates from the water to use as fertilizer
There are three basic methods of filtration: mechanical, biological, and chemical (below). Aquarium filtration systems often involve more than one of these methods and may utilize all three. Many tanks have an undergravel filter, shown below, which is a simple biological filter. Internal power filters (right), also provide biological filtration but can include additional media for purifying water by mechanical and chemical means.
- Mechanical filtration uses a filter medium, such as this filter wool, to sieve particulate waste from the water. The fibrous structure traps the waste, which can then be removed.
- Biological filtration involves the breakdown of waste by beneficial bacteria that drive the nitrogen cycle. These multiply in media, such as this foam sponge, and in the substrate.
- Chemical filtration relies mainly on activated carbon to eliminate dissolved waste from the water. Unfortunately, this process also neutralizes some medical treatments.
- Internal power filter An integral electric pump draws water through the filter unit, which contains one or several chambers housing filtration media inserts. After passing through the media, the clean water is returned to the main tank.
- Undergravel filter Air pumped through an airstone within an airlift tube draws water from below the gravel substrate. This forces the water through the gravel, which contains beneficial bacteria that break down harmful waste products.
AIR PUMP TIPS
- Fit a non-return valve in the airline between the pump and the tank to keep water from entering the pump.
- If the pump gets noisier, have it serviced or replaced.
- Never cover an external pump; this creates a fire risk.