XVII. Phosphate Control - Reducing Natural Accumulation
This article discusses the concepts behind Biological Methods & Chemical Methods
Phosphate is introduced to our tanks primarily from the food sources we offer our fish and coral, however, there is a very low level of phosphate in many additives as well. Phosphate is a phosphorus compound expressed as PO4 and is present in natural seawater at very low levels. While trace levels of phosphate present in an aquarium is not problematic, without proper export the levels of phosphate can accumulate to levels that will, in summary, impede the growth and generally stimulate nuisance algae growth. I would like to note there is a fine line between chemistry and biology. Here, biological methods focus directly on nurturing additional bacterial cultures while chemical methods refer to the application of any substance, organic or inorganic specifically to remove phosphates.
Biological Methods
We discuss beneficial bacteria a lot when discussing the nitrogen cycle, but there are also bacteria that aid in reducing phosphate as well. These bacteria, like nitrifying bacteria, tend to occupy anaerobic areas and require a carbon source to feed upon. This is because the consumption of phosphate is not done directly through gestation but instead through a complicated method called solubilization. These bacteria are known as Phosphate Solubilizing Bacteria(PSB), and they accomplish this passively as part of developing their natural slime coatings.
Many systems employ a reactor chamber of sorts which is filled with proprietary media for the bacteria to colonize. As the colony of bacteria consumes the chosen carbon-based food source, the slime coat grows along the surfaces they inhabit as a protective coating. This coating is primarily composed of the previously insoluble phosphate that the bacteria have absorbed and converted. The principle theory at work in these systems is that we allow the bacteria a protected area to colonize and establish a slime coat within. Periodically the media colonized is agitated so as to disrupt these films and introduce them to the water column of the reaction chamber. The protective slime coatings are then easily removed from the system using a protein skimmer.
Chemical Methods
While there are several proprietary systems employed to fill the niche of bacteria based phosphate control there are several more proprietary resins and additives that are marketed to reduce the phosphate levels of your tank. Many are added to the sump and changed on a regular basis although some involve the use of liquid additives. The various liquid additives have broad use instructions depending on brand consideration should be made to read the instructions thoroughly before purchasing. A bottle may last one aquarist x where it will only last aquarist y a much shorter time. It is important to make sure you will be adequately supplied as even brief stoppage of these systems due to running out can see spikes in phosphate and nuisance algae growth.
When referring to proprietary resins it is often a combination of components and rarely does this combination exclude granular carbon. Like granular carbon when uses on its own, these resins are exhausted in time and need to be replaced. The recommended time of effectiveness for most resins falls between thirty and ninety days before requiring replacement or in some cases recharging. When properly maintained these methods of control are equally effective as biological control options available. If more equipment is something you are not able to house then a liquid additive or resin based control method becomes an ideal solution to coral impeding, algae feeding phosphates.
Though of all the methods available, the following method is by far my favorite although it is very rare to see it officially endorsed by most. Vodka dosing is a fairly simple and straightforward method of nutrient control that combines both chemical(in the form of liquid additives) and biological(in the form of overall function) to achieve reduced phosphate levels. Best of all this method does not require any specialized proprietary equipment, media, or devices as most reef tanks already have a protein skimmer. While the cited literature has served me well in the past I have to admit that it is more suited for larger systems over one hundred gallons, it is not a matter of effectiveness as it is "weighs justifying means". Frankly speaking in my smaller systems with proper water changes, skimming and feeding practices phosphate is well managed and the need for phosphate control is not there.