Mechanical filtration is the extraction of debris from the water. This type of filtration removes large floating and suspended debris, and these filters may sweep up fry and small fauna.
Biological filtration is the culturing of beneficial bacteria that break down harmful ammonia into its less harmful form, though still detrimental to the fishes’ health when in high amounts—nitrates. Activated carbon, and clinoptilolite are the media that provide the removal ammonia and detoxification of the ammonia.
Filters are also important because they provide water movement that enhances oxygen diffusion and carbon dioxide expulsion.
Power filters are filters that hang on the back tank wall. This type of filter provides mechanical filtration by capturing large floating and suspended debris in the filter pads. These filters use removable cartridges that are placed in the filter and are discarded monthly. These cartridges have various filter media inserted in them to provide biological filtration. This method of filtration also provides surface agitation, which assists in gas exchanges between the water and the air.
Canister filters work in almost the same way as power filters. The differences are that canister filters have a far higher initial cost, but they make up for this by providing a series of different filter media to ensure superior filtration. These filters also provide circulation of water to assist in gas exchanges.
Undergravel filters are metal plates placed underneath the gravel to remove particles that have gotten wedge between and beneath the substrate. The bad thing about this type of filtration is that these filters can get clogged if too much debris is trapped in the gravel, so more frequent water changes are required.
Sponge filters are normally used in breeding tanks. These filters do not disturb the fry, eggs, or bubble nests that anabantoids create, and these filters will not suck up fry the way other filters do. These filters offer very little, if any, mechanical filtration, but they do provide biological filtration, which is more important for spawn and fry.
Perhaps more than you need to know, but doesn't hurt.
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