The salt water aquarist runs tests to ensure that the water quality in his/her aquarium is up to scratch. One of the tests should be phosphate, particularly in the case of a reef system.
Phosphate (PO4) is measurable in the sea and is a requirement of living organisms. It is present in a very small amount, 0.03 ppm (parts per million).
In the confines of an aquarium the phosphate level needs to be monitored. This is because the aquarist is continuously adding [tag-tec]phosphate[/tag-tec] as part of the essential maintenance, that is, feeding. This action is where the majority of the phosphate presence in the aquarium comes from. Without adequate control measures, the level will rise. Unlike some dangerous items checked for (for example ammonia) phosphate is not toxic. So there should be no problem, then? Yes, there can be.
Similar to [tag-tec]nitrate[/tag-tec] (NO3) phosphate is implicated in the growth of problem algae. In other words, it is a fertilizer. If the level gets too high expect trouble. In addition, excessive amounts of phosphate have been implicated in the inhibition of coral growth. So, particularly in a reef system, coral retardation and/or problem algae are definitely not required.
The very first action is obvious – do not overfeed. This advice is given for many reasons and this is definitely one of them. Continue with routine water changes, which are very beneficial again particularly to a reef but also to a fish only aquarium.
To be able to control phosphate the aquarist must know the situation, so include a test in the group tests that are done. Once the level is known and the control measures are found to be effective, the testing regime can relax somewhat. However, always be aware of the seawater condition. This applies to many parameters, not just phosphate.
If the test indicates a phosphate level of 0.03 ppm or less, there is no need to be concerned. In an aquarium, the best phosphate test result is probably ‘immeasurable’. Continue to test at least weekly until the trends of the testing are clearly seen. For instance, there may be a slow increase despite water changes.
If the test indicates a level of 0.10 ppm then the aquarist should consider control measures to reduce the level and keep it down. A reading of 0.25 ppm needs action without delay, as this is the point at which it is believed coral growth retardation will develop.
What action to take? The first, as mentioned but I’ll mention it again, is to critically examine the feeding regime. Next, consider increasing the amount or water changed at the routine water change. Make sure the seawater mix used at the water change is phosphate free, use R/O (reverse osmosis) water for the mix.
If the aquarist has a sump with a DSB (deep sand bed) or Plenum (raised DSB) installed, consider planting algae ([tag-tec]Caulerpa[/tag-tec]). Once the algae is established, it will sweep up a considerable amount of phosphate. Once well established, it should be harvested from time to time, leaving enough to allow re-growth
The easiest way perhaps to reduce and control phosphate is to use an anti-phosphate resin. The resin that seems to be most favoured is the iron based type. These are available commercially. Some of the best resins supplied are of a very fine grain and subject to clogging, obviously a bad state of affairs. If there is little water flow through the resin there will only be a small phosphate reduction. The method that I recommend is a fluidised reactor. These are simply a plastic tube of 2 or 3″ diameter, with a flow of water applied by an external pump, the flow moving from bottom to top. This holds the resin in suspension. It appears to be very gently bubbling at the surface. These reactors are available commercially and are very straightforward to use. The competent DIY aquarist should have little difficulty in constructing one.
All anti-phosphate compounds have a limited life. They can only remove X amount of phosphate from Y amount of seawater. The manufacturers state the limitations which allows the aquarist to make a simple calculation on the expected life span of the product, as the phosphate level in the aquarium seawater will be known. It is wise, however, to do a phosphate test from time to time, particularly when the resin is first used to tackle discovered phosphate. The reducing phosphate level can then be seen, and there is reassurance that all is well. Also make a written note of the date the compound was brought into use.
Using a phosphate removal compound is not an excuse to not be concerned about feeding. Controlling the input of phosphate to the aquarium as far as possible will extend the life of the removal compound, and in any case is simply good practice.