In an aquarium, filtration is the process of removing substances, such as fish waste products, debris or medications, from the water. There are several different ways that this can be accomplished, which will be outlined below


For the purposes of this article, we will use the following definitions:


BIOLOAD: the amount of waste produced by your fish that your filter needs to remove


FILTER - the physical device/system that circulates aquarium water across filter media.


FILTRATION - the process of removing waste/unwanted substances (chemical and/or particulate) from the aquarium water


MEDIA (FILTER MEDIA) - the substance placed into the filter that effects removal of unwanted substances from the aquarium water, in one of the 3 ways listed below.


WASTE: fish feces, uneaten fish food, ammonia (constantly excreted by fish - a metabolic waste, like urine)

3 Types of Media/Filtration

There are three types of filtration utilized in fishkeeping, either solely or, for maximum effect, in combination. They are as follows:


Physically traps (and thus removes) particles of waste matter, debris, etc., from the water Utilizes chemical processes to remove, modify, or trap harmful dissolved elements in the water Culturing and maintaining natural bacteria to break down waste substances in the water by means of the "nitrogen cycle"
  • Circulating debris
  • Ammonia
  • phosphates
  • medications, etc. (determined by type/properties of media used)
  • Ammonia
  • nitrite

Examples of filter media: 

  • Filter foam/sponge
  • filter floss
  • Zeolite
  • activated carbon
  • Phos-ban
  • Bio-balls
How It Works:
Acting like a strainer, filter foam/floss allows water to pass through while trapping debris that is too large to pass through the openings in the material Like biological media, chemical media has a large amount of surface area to maximize contact with the water. The media then "absorbs" via chemical recation, specific, unwanted chemical compounds in the water.

This media is designed to have a very large amount of surface area relative to its volume. This surface area is what beneficial bacteria will grow on.

  • Note that this media is inert, and does not remove ammonia on its own - it is simply a place on which ammonia-consuming bacteria can grow.
  • Requires regular cleaning/rinsing to remove debris/prevent collected debris from decaying
  • Requires periodic replacement as it becomes worn/dirty
  • Requires replacement once saturated with the element it is removing from the water
  • Some medias can be "recharged" and used multiple times before replacement
  • Media requires periodic (partial and gradual) replacement as it becomes dirty/clogged with debris

Types of Filters



As the name suggests, this filter is hung from the back of the tank, with the majority of the apparatus sitting outside of the water. Only the intake tube (A) and output spout (D) and hung into the tank.


HOW IT WORKS: Water from the aquarium is drawn up through the filter intake tube (A) by suction that is generated by an electric motor (B) which spins an impeller (not shown). The aquarium water is drawn up into the filter's reservoir (C) which contains the filter media, which filters out contaminants. As water is continuously drawn into the reservoir, it also continuously overflows back into the tank, via the return/output spout (D).



Being another power filter, this device opperates on much the same principles as the HOB filter above, except that it is submerged inside the tank, instead of hanging outside.


HOW IT WORKS: This filter works somewhat like a fountain - water is drawn into the filter at it's intake (A) but suction generated by a sealed electric motor (B) spinning an impeller (not shown). The water is then pushed up into the filter's reservoir (C) which contains the media which removes contaminants. The water then overflows out of the top of the filter and back into the aquarium at the return/output spout (D).