Phosphate Cycle
Phosphate is not too common, being part of fats and proteins, or as particulate phosphorus (found in detritus). It normally gets into ecosystems through primary producers like plankton.
Monitoring Phosphates
The main problem with phosphorus is that excessive amounts promote algae growth. To prevent this, keep phosphate concentrations below 1-2 ppm (parts per million) Phosphate levels must also be kept low for corals and reef inhabitants, since coral reefs naturally have low phosphate levels. To keep waters hospitable, keep phosphate concentrations below 0.02 ppm
To monitor and ensure proper phosphate levels, the water must be monitored using a reliable aquarium water testing kit
Managing Phosphates
Proper phosphate management is obviously quite important for the health of an aquarium. Some advanced filtration devices/chemicals can maintain very low phosphate levels (though this is not always needed)
Phosphates rarely need to be added to a reef tank and aquariums usually have too much. Instead, phosphates should be actively removed to prevent issues.
Ways to remove phosphate
Water Changes
The old-fashion, reliable way to remove phosphates (assuming purified freshwater is used in preparing new water). Even with all the other methods, at least some regular water changes are needed
Vacuuming the substrate
The most efficient way to remove phosphate is to remove detritus (such as with gravel cleaners). This prevents settled particulate organic matter from causing stockpiling of phosphates
Plants
A natural and popular way to control nutrients like phosphate is to plant aquariums thoroughly. Plants like seaweeds absorb nutrients like seaweed as they grow, storing them in the plant to be removed.
Because detritivorous microcrustaceans, such as copepods, heavily populate refugia, this method additionally helps to release phosphorus from detritus into phosphate.
Chemical filtrants
Some chemical filtrants absorb and store phosphate, such as ferric iron granules and aluminium oxide beads.
While ferric iron granules are strong phosphate absorbers, they are prone to clumping/compaction. On the other hand, aluminium oxide beads do not clump and can be held in a mesh bump and placed in an overflow box or sump for easy maintenance.
Chemical Filter Pads
Chemical filter pads provide even more control over phosphate levels by removing particulate matter as well as phosphate.