Chemical Filtration
Chemical filtration is included in this section, however contrary to popular belief, it isn't a necessary element of every filter setup. Chemical filtration is useful when removing medication, or other chemical related mishaps in the aquarium. The popular belief though, is that chemical filtration is needed in order to "polish", or clarify, the aquarium water. However, the vast majority of impurities that cloud the water are organic in nature (algae blooms, tannins from driftwood, etc). This myth is perpetuated because the most popular form of chemical filtration, charcoal, is relatively effective in removing organic matter as well.
The problem is, that charcoal is not the most efficient way to polish water. In fact, if it is left in your filter past its saturation point, it can actually start to leech impurities back into the aquarium. Without getting into the chemistry of it all, charcoal is effective in removing chemicals or medications, yet beyond that function, it has no other great uses. Therefore, other than assisting in medication removal, the vast majority of experienced hobbyists don't use charcoal often, or in some cases, at all.
Mechanical Filtration
The bulk of the work a filter performs is arguably mechanical filtration; the physical removal of impurities from the water column. Mechanical media affords you the convenience of removing the dirty media and then either cleaning or replacing it. As simple as that sounds, its an important part of maintaining clean water. Unfortunately, as much of work horse mechanical filtration media is, it also requires the most maintenance since, depending on your stocking and feeding levels, it can get clogged and dirty quickly.
Mechanical media hasn't really progressed that much over the decades. This is perhaps because its function is so rudimentary. For most aquarium filters, the mechanical filtration media provided is course sponges. Its worked well over the years in removing organic particulates, and is extremely reusable when cleaned and maintained properly.
Other types of mechanical filtration have surfaced recently, such as ceramic tubes that, when bunched together in a sack or in a certain section of the filter, work as a very coarse type of filter media in allowing the removal of larger pieces of organic matter to be captured without clogging to quickly. However, one of the most useful "new" (in the past 15-20 years or so) types of mechanical filtration is water polishing.
Ultra fine polyester (or other types of materials) have been used to get water clarity never before achieved when the hobby first started. With advances in technology, some companies have been able to manufacture micro-beads made from polymers designed to be very porous, allowing the capture even the most minuscule organic particulates. This often translates into water with amazing clarity. One of the more well know products of this type is Seachem Purigen.
Biological Filtration
 |
| Shrimp breeders utilize extra biological filtration to keep livestocks in breeding condition. |
Most aquarium keepers will agree that the single most important element in keeping a healthy and thriving aquarium is bacteria; nitrosomonas and nitrobacter to be exact. It is the colonization of these bacteria in aquarium filters (and to a lesser extent, on your aquariums surfaces) that will help maintain ammonium and nitrite levels. In fact, in some areas of the hobby, such as freshwater shrimp breeding, some hobbyists use a separate filter or unit, besides their primary filtration unit, specifically just for the colonization of beneficial bacteria.
In the past, media used for mechanical filtration served a dual purpose in both the removal of particulates and the colonization of beneficial bacteria. However, in the past 20 years, media dedicated to the colonization of bacteria have been used extensively. The technological advancement in this type of media has moved forward to some degree, but has remained relatively unchanged. The basic principle is to provide plenty of surface area for the bacteria to form, and then a steady flow of oxygenated water and food. Therefore, many hobbyists simply use dish or bathroom sponges (not used, of course) in their power or canister filter
In the next section, we'll discuss what type of filters will suit different situations best, and how water circulation can play a role in keeping water clean and oxygenated.
