Phosphorous is an essential component of living tissue, being the source of energy for the cell. Therefore, the notion that one can eliminate phosphate from the aquarium is false, unless one empties its contents completely and scrubs the glass clean, leaving a bare, dry aquarium, which isn't much fun to look at. Phosphorous in its many forms will always be there, in living tissue, in the substrate, in dissolved organic and inorganic forms, and in particulate detritus. Please refer to chapter 2, for additional information about phosphorous and its cycling in nature.
Though phosphorous is essential for life, a delicate balance between enough, and too much, exists in closed systems. Inputs must be matched by outputs and assimilation or precipitation. If phosphate is allowed to accumulate in usable organic forms it can trigger overwhelming blooms of algae. Inorganic phosphate (orthophosphate) has limited occurrence in the water since it is quickly consumed by plants, and readily blows off into the atmosphere as aerosol from the bubbling action in protein skimmers or airlifts (Spotte, 1979). It also readily combines with organic compounds or precipitates out of the water onto the calcareous substrate. The high pH in the vicinity of calcium hydroxide addition to the water also has a side benefit of precipitating phosphate t here with calcium. Chronic levels of inorganic phosphate in the water typically come from stored organic forms being broken down to release the inorganic phosphate, from sources that leach phosphate, from polluted tap water used as freshwater top-off, or as a result of heavy feeding.
Fish and invertebrate foods added to the aquarium are the most significant phosphate input for most systems. The fish must be fed in most small aquaria, though larger closed ecosystems produce sufficient algae and little crustaceans to provide enough, or more than enough, food for the fish. Still, most aquarists enjoy feeding their aquariums at least once in a while, and this is fine provided one doesn't feed too much. In this regard, we wish to point out again that liquid invertebrate foods that benefit non-photosynthetic organisms primarily, (don't confuse with liquid trace element supplements that are essential) are to be feci only very sparingly or not at all. Most of the cloudy water ends up as pollution that will
be mineralized by bacteria, instead of food benefiting target organisms. It is best to administer such foods by means of a pipette or eyedropper to spot-feed the target organism, thereby avoiding the practice of filling the whole tank with the cloudy solution.
Protein skimming removes inorganic phosphate from the water because the bubbling action blows the phosphate off into the air. Protein skimming also removes organic sources of phosphate very efficiently, depositing them in the collection cup along with the other components skimmed from the water. Thus a protein skimmer is a most important instrument in the control of phosphate in closed system aquariums.
Another potential input of phosphate to the aquarium is make-up or top-off water used to replenish evaporation. This daily addition of water can provide significant quantities of phosphate to the "closed" system aquarium. Not all tap-water or well-water contains phosphate, but many urban and rural areas have phosphate in the water in both organic and inorganic forms. If you are using this water to make kalkwasser then the high pH of this solution may result in the rapid precipitation of any remaining phosphate, in the form of calcium phosphate. Nevertheless, the use of a water purification system for one's top-off wrater is a good means of insuring the water's purity. Reverse osmosis and deionization systems are readily available now through numerous aquarium industry companies.
We mentioned earlier under the topic of chemical filtration that some types of activated carbon can leach phosphate into the water. We suggest that aquarists routinely check newly purchased batches of activated carbon with a phosphate test kit as a precaution (see the section on activated carbon in chapter 5).
One additional input of phosphate comes from airborne dust. This can be especially significant for aquariums located outdoors, and is more significant for aquariums without covers of course. In most indoor home aquariums the phosphate input from airborne dust is slight. Covers, mechanical filtration, and protein skimming help to counter this type of input for aquariums located where there is a lot of airborne dust.
Exports of Phosphate
The use of herbivorous snails is a valuable aid in the export of phosphorous from the aquarium. Algae growing on the rocks and
walls of the aquarium remove phosphate from the water and the snails graze the algae. Their little fecal pellets contain some phosphate then, and the removal of these pellets through mechanical filtration or siphoning of settled material is a way to remove the phosphate from the system.
Mechanical filtration is not essential, but it does sxeatlv assist in the
export of particulate organic phosphate. Without mechanical filtration or other removal systems such as settling filters, the particulate material must be broken down by bacteria and microorganisms, or consumed by various filter feeders and detritivores. Their consumption of detritus plays a key role in the denitrification process, (see previous section on nitrate control).
The detritivores also play a key role in substrate management. Gobies sift the sand for detritus and the small crustaceans that feed on detritus. The little crustaceans multiply well in thick substrates, as do numerous species of polychaete worms that feed on particulate matter. These organisms all play a role in the reduction of available phosphate in the system, and prevent the sand from becoming a dead muck zone where detritus merely accumulates.
Another means of phosphate control is effective, but not natural. There are numerous brands of phosphate removing filter media on the market, and they all work reasonably well. We wish to rf wf emphasize that proper aquarium technique prevents the accumulation of detrimental levels of phosphate. The routine addition of calcium hydroxide solution precipitates phosphate from the water. Combined with protein skimming and proper aquarium husbandry the phosphate level is easy to control without dependency on phosphate removing media. Nevertheless, these media do have some use in emergencies, (see subject heading Dinoflagellates in chapter 10).
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