There are many thoughts regarding the three types of filtration and their importance with respect to efficiency and effectiveness, or lack thereof in a saltwater closed system environment. The three types of filtration are BIOLOGICAL, CHEMICAL and MECHANICAL! Each of these filter schemes is responsible for different methods or ridding your tank of contaminants, food waste, pollutants, detritus, ammonia, nitrites and nitrates and possibly aiding in the reduction of nuisance microalgae, cyanobacteria, diatoms, and silicates.
BIOLOGICAL FILTRATION consists of bacteria, both aerobic(requiring oxygen) and anaerobic(not relying on oxygen) found within the benthic(substrate) areas of our tanks, as well as on and within the pores of live rock. Worms, microscopic crustaceans, and protists are also responsible for the decomposition of both organic and inorganic waste. Heterotrophic (chemoorganotrophic) denitrifying bacteria converts amino acids to ammonium, a process known as mineralization.
MECHANICAL FILTRATION is a process which employs filtration by means of a protein skimmer, conventional hang- on or cannister filter. This method of filtration aids in the trapping and removal of particulate matter suspended in the pelagic(water column) area of your tank. These filters will help to rid your tank of turbidity, detritus, uneaten food stuff as well as other fine particles and floating matter., which will help with the overall quality of your water.
Now, in my opinion, a protein skimmer (foam fractionator) is an essential component of a saltwater tank, especially a reef tank. Cannister and conventional hang-on filter styles, I feel, are a waste of money! These filters come up short in terms of the overall cycling process. Their ability to remove ammonia, and nitrites is evident and beneficial, however, their benefits regarding the cycling process stops there. Nitrate levels, many times, become elevated to possible dangerous levels as the filter media and filters become clogged and dirty, thus becoming a detritus and waste collector which will leach back into your water column, and reduce water flow, ultimately decreasing their ability to effectively clean your water. A protein skimmer replicates the natural filtration process brought about by waves as they crash against the beach. Foam generated by waves and deposited at the shore, is natures way of cleaning and removing waste and excess nutrients from the oceans and reefs of our world. There are reef and fish only tank set-ups that forego the mechanical filtration process all together. Though this is accepted method and has proven successful, I would shy away from the idea of employing this tactic, especially, the use of a protein skimmer. The hang-on and/or cannister ommitance is allowable, though the skimmate collected by a protein skimmer, the addition of dissolved oxygen, and the ability to release inorganic phosphates (orthophosphates) into the air through gas exchange and microbubbles should be enough reasons to implement a skimmer to your tank set-up.
The use of a deep sand bed, algal scrubbers, refugiums, live sand and rock also enables a tank to be set-up without the need for mechanical filtration. Each of these techniques comes with its benefits and drawbacks, but I would would not hessitate to experiment with one or more of these options.
CHEMICAL FILTRATION is an effective means of removing impurities such as DOM (dissolved organic matter). Activated carbon is a popular and effective means of ridding organic matter such as Gelbstoff(yellowing color of tank water) as well as toxins released by Octocorals(soft corals). These toxins can prove detrimental to stony corals especially, by stunting their growth and altering their overall health. Carbon use is ultimately associated with the amount of photosynthetic available radiation(PAR) available to ahermatypic corals(containing zooxanthellae-requiring light). Carbon will aid in the clearing up of your water by removing turbidity and DOM. These particles and chemicals, can influence coral growth and success based on the amount of these refractory compounds found in your water column, decresing the amount of beneficial light required by corals that contain zooxanthellae. Zooxanthellae is a bacteria that lives in a symbiotic relationship within coral tissue. It is brown/tan/cream colored and requires light, adsorbed by ahermatypic coral tissue much in the same way as a tree requires sunlight to carryout photosynthesis. In return, the zooxanthellae feeds the coral ammonium, which is the end result of the photosynthetic process. Carbon doesn’t come without is drawbacks as well…it removes chelated substances such as Iodine, and other trace elements. Medications will quickly be consumed as well, which is the reason why carbon should be removed when dosing medications. Carbon use will increase the amount of harmful radiation that is received by corals. Some corals such as Acropora contain pigments in their tips to help repel these harmful rays much like a sunscreen protects us from the suns harmful rays. Too much light without proper acclimation of corals to the light change will cause bleaching. Bleaching is a process brought on by an overabundance(supersaturation) of oxygen in a corals tissue created to much light and the corals zooxanthellae’s inability to breakdown this excess light. When a coral receives an overabundance of oxygen(harmful in excess amounts), it will disperse its zooxanthellae from its tissue as a last ditch effort at survival by conserving its energy. Once a coral has released its zooxanthellae, often the coral will take on a white coloration, hence the term-bleaching. Certain corals may take on other colors as well as they contain chromatophores(pigments) responsible for solar screening and light enhancement.
!!!!!Carbon MUST be replaced frequently, to reduce the chance of leaching back into the water contaminants that it had previously removed.
In concluding, there really isn’t any right or wrong filtration scheme as long as your water quality remains optimal! The number and size of your livestock will ultimately alter your water parameters, therefore, filtration will need to be addressed for the long term success of your tank and its inhabitants! Which ever method of filtration you chose or number of filtration options you employ, take the time to research all the options available to you, to ensure that you make the right decision for both you and your tankmates.