Aquarium filtration is essential for maintaining water quality, removing waste, and providing a healthy environment for aquatic life. There are three primary types of aquarium filtration, each serving a specific purpose.

Mechanical Filtration:

Intended use: Mechanical filtration is designed to physically remove solid particles and debris from the water, such as fish waste, uneaten food, plant matter, and other visible particles. It helps to keep the water clear and prevents the accumulation of debris that can lead to poor water quality.

Filter Media: Mechanical filters use various filter media, such as sponges, filter floss, or pads, to trap and capture particles as water passes through the filter. The filter media should be regularly cleaned or replaced to maintain its efficiency.

Particulate isolation:  The filter is designed to remove particulate matter that is of a certain diameter.  Some particulate filters are designed to remove particulate matter as small as 20 um (micrometer).  Smaller particulates are let through and will precipitate from the water to the aquarium floor.

mechanical filters are not intended to remove virus’ or bacteria.  Bacteria fall into the range of .2 um to 10 um.  As a reference, human hair is approximately  50-100 um in diameter.

Biological Filtration:

Intended Use: Biological filtration is crucial for removing harmful nitrogenous compounds, like ammonia and nitrite, from the water. It helps to establish and maintain a colony of beneficial nitrifying bacteria that convert ammonia into nitrite and then into nitrate, which is less toxic to aquatic life.  This process is referred to as the Nitrogen Cycle.

Filter Media: Biological filtration typically utilizes porous media with a large surface area, like ceramic rings, bio-balls, or foam, which provide ample space for beneficial bacteria to colonize.  This filter operates by exposing as much water as possible to the surfaces where algea and bacteria have colonized.

Living filter: The biological filter is a living breathing mass of bacteria and algae.  The success of this filter depends upon keeping the algae and bacteria alive.  Consequently, care must be given to the living conditions of the filter.  The aquarist should monitor temperature, humidity, and light to be certain the algae and bacteria can survive.

Chemical Filtration:

Intended Use: Chemical filtration is used to remove dissolved impurities, odors, and medications from the water. It helps to purify the water by removing toxins and chemical substances that may not be effectively eliminated by mechanical or biological filtration alone.

Filter Media: Activated carbon is the most common filter media used for chemical filtration. It has a high surface area and can adsorb a wide range of substances. Other chemical filter media may include zeolite, which can remove ammonia, and resins that target specific pollutants.

Chemical isolation: This type of filtration is not necessarily needed 24×7.  Often, this type of filtration is engaged directly following a water exchange or directly following a tank medication event.  Bear in mind that this type of filtration becomes increasingly less effective the longer it is in use.  This filtration method works on the premise of molecular attraction.

Activated charcoal and other resins have available surfaces to which other compounds will attach.  As more compounds attach themselves, the available carbon surface areas diminish in availability.  The filter becomes saturated and requires replacement.

There are some filter designs that accommodate multiple filter types.  These filters will provide a pad or sponge on one side and a charcoal filter on the other.

The difficulty with the combination filters is that  mechanical filtration may become saturated with particulates before the activated charcoal has become saturated.  Because the two are physically connected they have to be replaced at the same time.

This is less of a concern when considering a biological filter.  Often these filter types are designed with particulate catch areas that can be replaced or cleaned independent of the biological area.  Bear in mind that biological filters, when healthy, may give off a “swamp-like” (sulfur compounds) odor as the bacteria processes the nutrients in the water column.

Physical filters come in a wide variety of shapes and sizes. Generally there are four types and within those four types there are any number of styles.

• Power Filters (Hang-On-Back Filters): These filters often combine mechanical and biological filtration and may include a compartment for chemical filter media.
• Canister Filters: Canister filters provide all three types of filtration (mechanical, biological, and chemical) and offer high filtration capacity for larger aquariums.
• Sponge Filters: Simple and air-driven, sponge filters are primarily used for biological filtration in small aquariums or as additional filtration in larger setups.
• Undergravel Filters: These filters use a perforated plate under the gravel to promote biological filtration through the substrate.

A well-balanced combination of all three filtration types ensures a healthy and stable aquarium environment. Regular maintenance, such as cleaning filter media, changing water, and monitoring water parameters, is essential to maintain the efficiency of the filtration system.