Filtration

Aquarium filtration

This page is an extension of information found on Aquatic animal life support, one of the three essential animal care pages!

Filtration location

Oooh, fun rhyme! In small tanks that are not connected to any other tanks, like ones you may have in your home, there's likely a little component that hangs off the back and contains filtration equipment.

In larger aquariums or aquarium systems that contain multiple tanks, there may be a tank designated as a sump. The sump likely doesn't contain habitat or animals, and just houses filtration equipment. Pumps push water through equipment and back and forth between tanks and the sump.

Types of filtration

There are four general types of aquarium filtration. I'll give a bit of information on each before some examples below.

Mechanical filtration is the removal of visible particles (or particulates). This is ideally the first stop for water when it leaves an area with animals, because it's the most significant cleaning step.

Chemical filtration removes dissolved compounds, that are much smaller than particulates. This is done through the forms of sorption: ion-exchange, adsorption, and—the one you're familiar with—absorption. (Yes, adsorption and absorption are two different words!)

Biological filtration is essentially the nitrogen cycle, but in a very small aquatic environment. When humans excrete liquid waste (… pee), our bodies put a lot of energy into transforming and diluting compounds that could be harmful to us. Aquatic animals, on the other hand, typically excrete nitrogen-based waste in the form of ammonia, which easily becomes toxic when concentrated. As animals are in a limited amount of water, you could see this becoming a problem…

To eliminate ammonia from aquarium systems, we grow bacteria that "eat" ammonia, turning it into nitrite. Nitrite is still comparatively toxic, so there are more bacteria that convert nitrite to nitrate. With nitrogen-based waste stored in the form of nitrate in the aquarium system, it can be non-urgently managed.

"Sterilization" is in quotation marks because it's an exaggeration. We can use two different processes to kill tiny organisms like bacteria, viruses, protozoans, algae, etc. we don't want in an aquarium, but it's not truly being sterilized when it's attached to an aquarium housing animals. More like disinfected… maybe.

This is the sump for a smaller aquarium of around 200 gallons. It is located underneath the exhibit and hidden behind a removable panel. The water was chilled to 55 °F for coldwater animals, which is why the outside is so wet from condensation! This system did not need sterilization.

Examples

Biological

Biological is by far the most important so let's look at that first. The equipment used for biological filtration isn't all that fancy, because this process is really just about the bacteria. Usually, the materials used are called bio-balls, which are plastic spheres that are significantly cut out to create more surface area for bacteria to grow on. All shapes and sizes exist for different uses, so plastic material can generally be referred to as bio-media (get it? "Biological media").

Technically, all surfaces—including sand or gravel, walls, and pipes—can be colonized by the bacteria, but this practice of designating media for its use ensures that bacteria are appropriately kept alive. Bio-media can be in containers, or bagged and transferred to other systems to move bacteria around. It can be set aside if and when aquarium systems are fully disinfected, which would kill the bacteria otherwise.

Where does the bacteria come from to begin with? If there is no way to use the bacteria from another system, commercially bottled bacteria or commercially packaged "live" sand or rocks can supply it.

Mechanical

Some of the most common equipment used to remove larger particles are known as filter bags (or, more affectionately, filter socks). "Dirty" water leaves a tank containing animals and falls into the sump, passing through the filter sock. (The same materials can also be used to make flat pieces called "pads" or something similar.)

Filter socks need to be removed and cleaned, usually sprayed out with a hose. Some facilities may use a dishwasher or washing machine to clean many at a time.

  • Slide title

    Dirty socks

    Button

  • Slide title

    Clean socks!

    Button

On larger aquarium systems, one device that handles much larger volumes of water is called a rapid sand filter. Water is pumped from a tank with animals or from the sump through the sand filter, which uses fine sand—or tiny plastic or glass balls—to catch particles. To clean out what the sand has caught, the direction of water is reversed, and water passes up through the bottom of the sand filter to push waste out of the sand and out of the system. These are commonly used on pools—as in the chlorinated ones that humans swim in!

Large sand filters stacked in pairs that filter water in a 500,000-gallon system.

Chemical

The most common example, a foam fractionator (or protein skimmer), is discussed on Aquatic animal life support. That device uses the process of adsorption, allowing fine bubbles to remove molecules, microbes, and other microscopic things from saltwater aquariums.

A frequent method of filtering through absorption is the use of activated carbon. Manufactured from organic sources (such as nut shells, wood, bone), water is pumped through a filter containing activated carbon, which absorbs metal ions, medications post-treatment, and odorous or colorful compounds that impact water clarity. This media must be replaced as its capacity to absorb decreases.

Ion-exchange is not used often, and isn't really practical in saltwater since it contains so many ions. Think water softeners!

Commercially available activated carbon

"Sterilization"

There are two methods used to kill microorganisms (including bacteria, viruses, and potential parasites) in aquarium systems. They don't really sterilize, but hopefully do help disinfect. Ultraviolet sterilizers contain a light bulb that produces UV light inside of a chamber, which water is pumped through. This short exposure to UV light has the potential to kill unwanted organisms, decreasing their load to help prevent infection in the fishes and invertebrates.

The other method is through the use of ozone, which is an oxidizer like bleach (chlorine) and hydrogen peroxide. (Pure oxygen gas is O₂ and ozone is O₃, it contains an unstable bond.) There are different ways to scale it, but as part of an aquarium system, concentrated ozone levels are added to a small volume of system water in a container called the contact chamber. While the ozone is in contact with the water, it kills microorganisms inside of it. Once water leaves this chamber, there are multiple ways to ensure that ozone is not transported back to where animals are housed. (Also, as ozone is unstable, it breaks down quickly.) The concentration for O₃ disinfection in aquarium systems is less than 2 ppm (parts per million).

Share by: