Mechanial Filtration

• Mechanical filters simply remove solid floating particles from the water, such as uneaten food. Aquarium filtration company Algone (alonge.com) recommended that filter cartridges should be changed every two to four weeks to ensure they are effective. Generally aquarium owners should not rely solely on mechanical filtration as, once waste particles have started to decompose, they will not be caught by a mechanical filter. Various types of mechanical filters can be used, including paper cartridges, sponges and floss.
  
  

Chemical Filtration

• Helping to remove waste products that have already dissolved into the water, chemical filtration will not be caught in a mechanical filter. Aquarium experts such as those at aquarium information website Fish Lore (fishlore.com) generally recommend using granular activated carbon for chemical filtration. This is carbon that has been heated with steam to very high temperatures, causing it to become porous. These pores act as a trap for waste in the water at a molecular level. Working out the right amount of carbon to add to the water can take experimentation. As a starting point, in his guide to aquarium filtration (FAQ.thekrib.com/filters) Bruce Hallman suggests 1/2 cup per 20 gallons of water, changed once a month.
  
  

Biological Filtration

• One of the most important types of aquarium filtration is biological filtration. Filtration company Algone (algone.com) recommends it for all aquariums. Rather than simply removing waste from the water, biological filtration concentrates on establishing beneficial bacteria. When an aquarium owner starts a new tank, he should work to establish good biological filtration, which is a natural biological cycle in which ammonia in waste will be broken down by good bacteria. To establish the process, aquarium owners need to ensure that the tank has adequate oxygen and that surfaces such as rocks are available for the bacteria to attach to. If the number of fish in a tank is kept low, the fish could survive with biological filtration only.
  
  

Types of Filters

• Various kinds of filters can be used for all the filtration processes listed above. One of the simplest and most common is the corner filter -- a basic filter placed inside the tank, which water is forced through. It is both a mechanical and chemical filter and often a biological one, too, as bacteria settles on it. As they are cheap and easy to fit, Bruce Hallman recommends them for new fish keepers in his guide to aquarium filtration (FAQ.thekrib.com/filters). Under-gravel filters are also common and work in a similar way, but they sit under the gravel. However, they can lead to gas pockets under the gravel that can harm fish. Power filters hang on the back of the tank and siphon water through and can be both chemical and mechanical. Canister filters are similar but more powerful.