Filters and Filter Materials

Almost all of us encounter filters in one way or another in our daily lives. We pour water through a filter jug, change the cartridge in a purification system, or simply breathe air that has passed through an air conditioner filter. But what is really behind these familiar actions?

A filter is essentially a barrier whose task is to separate a mixture by retaining some components and allowing others to pass through. It works like a very selective gatekeeper. The material that this guard is made of is the filter material. Its properties determine what will be stopped — large dust particles, tiny bacteria, or chemical impurities.

The variety of these materials is striking: from simple metal mesh and paper to complex membranes and sorbents such as activated carbon. The choice of a specific type depends on what we are fighting against — sand in water, exhaust gases, or sterility in a hospital. Understanding the basics of how filters and materials work helps you make the right choice, whether for your home, car, or business.

Classification of aquarium filters

Graphical classification of aquarium filters by operating principle – electric and air

Electric filters come in a huge number of modifications capable of solving any task in both amateur and professional/commercial aquarium keeping. The advantages of this group include high performance, versatility (they can provide all types of filtration), and a wide range of applications (they are available for all types of aquariums). They are divided into internal and external, i.e., located inside or outside the aquarium.

Among air filters, bottom and airlift filters are the most common. Their advantages include simple design, low cost, and low energy consumption. Their disadvantages include modest performance, which is why they are not recommended for use in large aquariums. They are located exclusively inside aquariums.

Types or methods of filtration

There are three main types (methods) of filtration: mechanical, biological, and chemical. It is worth noting that even the simplest filters (electric or air) perform two types of filtration at once – mechanical and biological, and the more expensive ones perform all three, so for a home aquarium, it is quite enough to install just one filter that is suitable in design and cost to solve all water purification tasks.

1. Mechanical filtration

Purification of water from solid suspensions (sediment from new soil, fish excrement, pieces of dead leaves, uneaten food residues, etc.) using porous materials in the filter. The criterion for the quality of mechanical filtration is water transparency.

2. Biological filtration

Purification of water from toxic nitrogen compounds (ammonia, ammonium, nitrites) produced by fish during their life activities was mentioned above. Harmful substances are processed by beneficial bacteria that naturally inhabit the surface of filter materials or special carriers provided in the filtration system, such as bio-balls, sponges, etc.

3. Chemical filtration

Purification of water from dissolved organic compounds such as ammonia, methane, hydrogen sulfide, drugs used for the prevention and treatment of fish, etc. This partly duplicates the work of biological filtration, but unlike the latter, it has a wider range of applications and is based on a chemical reaction between organic compounds and special fillers (activated carbon, zeolite, phosphate absorbers) in the filter material. A side effect of some fillers is a change in the hydrochemical composition of the water.

Filters are devices that clean liquids or air by trapping dirt, dust, bacteria, and other harmful particles. The main work is done by the filter material through which the flow passes. It varies from simple fabric to complex synthetic membranes, and each type is suitable for its own task, whether it is water purification, indoor air purification, or equipment protection. The main thing is to choose the right filter and material for specific conditions, otherwise it will be of little use.

What should you pay attention to?

The main parameters of the filter are the volume of the filter medium and the flow rate (the speed at which water is pumped through the filter) — measured in liters per hour (l/h).

The capacity of the filter you buy should match the size of your aquarium. Don't go for filters that are too big, as they create strong currents in small aquariums.

A filter with a capacity of 300 liters per hour will completely filter all the water in a 600-liter aquarium in two hours, but in a 50-liter aquarium, it will take about ten minutes. From the fish's point of view, this is the same as living in a washing machine.

However, insufficient water flow through the filter can cause the water to become cloudy, and insufficient filter media will cause the filter to clog quickly, so a filter with adjustable power is the best option.

What types of filters are there?

All the variety of filters can be divided into several types, listed below. They are arranged in a hierarchy, with the simplest and cheapest at the top and the most technologically advanced and effective, but expensive, at the bottom.

Sponge airlift filter

Consists of a perforated plastic tube with one or more sponge cartridges attached to it. Air is supplied through the bottom, which rises and carries water with it, thus creating suction. Water enters the tube through the sponge, leaving various debris on it. It primarily performs biological filtration and, to a lesser extent, mechanical filtration, since the porous structure of the sponge creates a huge area for colonies of beneficial bacteria to colonize. Many aquarists constantly force the sponge filter to work somewhere in the corner of the common aquarium, thereby maintaining the biological maturity of the sponge, so that later, when necessary, it can be used in a quarantine or spawning aquarium. For more details, see the article “Air lift filter with sponge as the best biological filtration tool.”

Bottom filter

Primarily intended for biological water purification. Cheap, durable, virtually maintenance-free, and inconspicuous in design. However, there are a number of specific features that make it a poor choice for a novice aquarist. Since the aquarium substrate acts as the filter material, it is important to choose the right size of soil particles and depth. In addition, decorative items and dense plant roots will impede water flow, creating “dead zones” where silting will occur with unpleasant consequences in the form of methane or hydrogen sulfide bubbles.

Internal cup filters

One of the most popular types of filters due to their excellent price/performance ratio. They perform both mechanical and biological filtration, come in a wide variety of sizes, and can be installed vertically or horizontally. The best choice for small (up to 100 liters) and medium (up to 200-300 liters) hobby aquariums.

Hang-on filters

As the name suggests, they are suspended from one of the aquarium walls. Suitable for tanks from 20 to 300 liters, they are capable of performing all three types of filtration. Easy to use, the cartridges with filter materials are located outside and are easily accessible for replacement or cleaning. The purified water returns in a kind of waterfall, rather than a stream of water as in a cup filter, which minimizes the internal flow in the aquarium, which is useful when keeping certain species of fish that originate from stagnant water bodies, such as killifish and labyrinth fish. Hang-on filters have a minor drawback due to their design: the aquarium must always be more than 2/3 full, otherwise the water intake tube will simply not reach the water or will not be submerged enough, which will reduce suction and performance.

Irrigation or irrigated filters

Mainly used by professional aquarists in commercial aquariums. The main task of such filters is biological purification, however, manufacturers often equip them with auxiliary materials for mechanical and chemical purification. The filters are located outside, and the design includes several compartments usually filled with special bio-balls, which are constantly irrigated with incoming water, thus creating the most comfortable conditions for the development of a colony of beneficial bacteria — a moist environment and constant contact with air. Irrigated filters are bulky and highly specialized, so they are unlikely to be suitable for an amateur aquarium.

External canister filter

They provide all three types of filtration and excellent water circulation, and are virtually silent. They come in a variety of models for both small (up to 50 liters) and very large aquariums (over 1000 liters). Their performance does not depend on the water level; they work effectively even in partially filled tanks and paludariums. Additional options can be added to the design, such as oxygen saturation, ultraviolet disinfection, water heating, and more. A canister filter can combine almost all the necessary aquarium equipment, with the exception of the lighting system. It all comes down to price — this is a rather expensive type of filter, but it is the most effective and productive.

As you can see, choosing a filter and its “filling” is not just about buying a device. It is a conscious decision that directly affects the quality of water, air, or other resources in your home or workplace. The right filter material is the heart of the entire system; it is what does the main work.

Therefore, before making a choice, you need to clearly understand what exactly you need to clean the environment from. Sometimes a simple mechanical filter is enough, and in other cases, a multi-stage system with different materials is necessary. Focus on your specific tasks and requirements.

Ultimately, a good filter is a reliable and quiet helper. It ensures cleanliness, preserves health, and extends the life of your equipment. By taking the time to choose now, you will ensure peace of mind and high-quality results for a long time to come.