Biological Filtration vs. Mechanical Filtration

Biological filtration is the term used to describe beneficial bacteria. It is established during the initial cycling of the aquarium and relies on micro-organisms to process toxins into less toxic matter. This process happens continually as bacteria break down ammonia and nitrite and converts them into a less toxic compound call nitrate. Biological filtration is essential and needs to be established adequately. Live rock and sand are examples of biological filters. In theory you could maintain with these alone, but the fish population would be restricted in number and variety.

The beneficial bacteria need oxygen-rich water and surfaces to grip. They will attach to any surface in an aquarium – filter media, rocks, gravel, and plants included. This presents special issues when treating the fish population or cleaning the tank. The beneficial bacteria must not be wiped out. If a fish needs antibiotics, create a “hospital tank” to prevent the antibiotics from killing the bacteria. In a salt water tank you can maintain it using only a protein skimmer and biological filtration.

Mechanical filtration removes solid particles such as fish food and excretions from the water. It does not convert ammonia, nitrite, or nitrate. This is usually done by a filter that is placed either in or just outside of the aquarium and is usually run by an air pump. It simply is a means to remove free-floating waste before it decays.

Natural and synthetic sponge-like materials are housed inside the filter. A pump or bubble flow draws water into the filter where it is circulated through the media and back into the tank proper. As the filter becomes clogged with debris, water flow will be reduced – this is how you know it’s time to change or clean the mechanical filter.

Mechanical filtration is only beneficial if the filter material is replaced every two to four weeks. To save money on replacements you can also rinse or use alternative filter material such as filter floss, which is cheaper than cartridges. The most common filter media are paper cartridges, sponges and floss. It’s also important to use a siphon to remove particles that become trapped in the gravel. To protect your biological filter, only change a small portion of the water at a time.

Striking a balance between your biological filter and mechanical filter is the key to successful filtration. It’s important that you don’t wipe out your biological filter when cleaning the tank. It’s also important to have an adequate mechanical filter so that your system is not overwhelmed with large waste particles. Balance will keep your fish happy!