I thought we could take a little look at Phosphate/Phosphorus and how we see it and deal with it in our tanks. So hopefully I can put some info out their with out screwing it up to bad.
Ok so when we look at Phosphate we have to look at the number of different ways it is in our tanks.
Dissolved inorganic phosphorus
Is biologically available and essential to plants and algae. It is mostly dissolved phosphates. It enters the aquarium from tap water, sometimes from water treatments like pH buffers, it is wasted through the gills and kidneys of animals, it comes on seafood as a wash/enhancer, on food as perservatives, In our salt mixes and is produced in aquariums from organic phosphorus by bacterial and algal phosphatase activity. It is converted to particulate inorganic phosphorus by sorption and precipitation.
Particulate Inorganic Phosphorus
Is mostly not biologically available. It is phosphate associated with phosphate minerals and adsorbed on metal hydroxides and other solids in the aquarium. It enters the aquarium mostly in fish food and animal feces and it can be removed by siphoning out detritus and cleaning filter media. It also enters our tanks by adding argonite sand and LR. It is formed within an aquarium by sorption and precipitation of dissolved inorganic phosphorus.
Dissolved Organic Phosphorus
Is biologically available to bacteria and possibly to algae. It enters the aquarium from animal waste. Bacterial and algal phosphatase activity convert dissolved organic phosphorus to phosphates.
Particulate Organic Phosphorus
Isn't available to plants and algae, but is available to animals. It enters the aquarium as plant detritus, fish food and feces. It can be removed by siphoning and filter cleaning. It is converted to dissolved phosphates by phosphates activity. The phosphatase activity is partly due to detritivores but also to bacteria and possibly algae.
Ok so there are the basic forms that we see. Now lets take a peek on what it does when it gets into our tanks...
Phosphates In Our Tanks
When available P enters the tank, bacteria are the first inline, they immediatly go after it. Now bacteria just can't eat it, they have to create a liquid soup (for lack of a better word) with in this soup they can disolve and store P and use it. When they do this they allow for the growth of more bacteria and thus more of this bacterial bile. It just keeps growing and growing. Now these bacteria and their bile are covering all surfaces of our reef tanks, from rocks to sand to power heads. Anything that may be percipitated out of the water column (say such as kalk and P) will not make it past this biofilm of bacteria and bile. They need it and want it and not much will stop them. So even if its percipitated as a solid it will be broken down with in hours. So this is happening everywhere in our tanks constantly. In the rocks this is also the case. The bacteria continue to mass and to create more of this biomass with in the rock, as it masses it begins to move to the outer surfaces of the rock, we call this bacterial tugur. Once it reaches the surface of the rock it begins to shed off, most folks call it detritus, it is actual bacterial flock (died bacteria, bacterial shells, unused organics, particulate dust, and bacteria fuilds) it is also heavier then water so it will sink once blown free on the surface, if not blown of it will become food for algae (usually). This process is a constant 24/7/365 type of thing.
Ok in sand or similar sediments, the same concept with one BIG exception. With the population growth of the bacteria and the soup it uses and needs in which to live it also pushes out and up. The problem is that our tanks have side walls and a bottom, so when that is hit it pushes in the only direction left...UP. As time goes by this mass of bacteria, soup and all of the above begins to reach the surface. Once there, it will begin to leech into the aquarium. Now this P in all its forms and conditions is still trapped with in its biofilm and not available to our test kits (well some of it is, but only if you draw the sample from the bed). Once on the surface it will become available to higher organisms such as algae. Cyano first then the more common types including hair algae. Since the sand is not a fixed thing this means that it will not all come up at once. First over here, then over there, then all over the damm place and then all over everything.
Sediment has no method for dealing with it, so it doesnt matter how well set up the thing is, it does not work biologically. What its will do through the above mentioned processes is to facilatate it to be removed. Translated= it will bring the available P to the surface where it will be converted to OP by absobtion into the tissue of algae from which you can harvest.
Ok so now we know the enemy has been identified and we know the different forms it takes and we now have an understanding of how it enters the tank, What do we do?
Dealing With Phosphates
What we put in:
Well there is no one stop shop here. P is complex and it comes in various forms so we have to approach the battle on many different fronts in order to keep the balance. The best way to start is to watch our input, what do we add to our tanks that has a high ammount of P.
- Some folks water comes laidened with P, so the use of an RO/DI unit can deal with that.
- Alot of foods we buy can be laidened with P in various forms specially foods that use preservatives (frozen and alike) but flakes and such can also have it. SO best if we take some of the food we add and put it into a small glass, mush it up and then do a P test on it, that will tell us right away.
- Some salt mixes come with alot of P that is readily dissolvable. So perhaps a check on the contents of said salt to make sure the P is in balance.
- Some of the media used in calcium reactors can also put P into your tank. Any medias that have shells in them (ARM I believe?) will introduce P as it melts as when animals create their shell they use P in the process. Also media that are Argonite based and from terristral source will have P bound to them through runoff and so on.
So that is the input side, but its only a part in the overall fight, but even then it will still be produced and will still be in our tanks. So in the next fight, we need to break it down into its various forms and take it from there.
The Stuff thats in their already:
Organic bound up in bacteria and algae are associated with extra food/detritus (as in bacteria are on it and eating it and creating their soup). So if we remove this stuff we remove it in many forms. These forms are:
Particulate Inorganic P (ie: microscopic argonite dust that has attached to organics)
Particulate Organic P (ie the food or waste blob, baterial soup, bacterial floc and so on)
Disolved Organic P (more parts of the soup and enzynes used by bacteria and or P that is in transistion)
Organic P (the little bast*** bacteria and cyanos that are loaded with it) .....by simply syphoning/skimming/socking and whatever from the tank directly prior to it entering into any cycles.
So now we can look at Ferric Oxide (a Popular P absorber). At a certain point in the P cycling and all the other processes listed previously, their are points where the P is inorganic and available. This is where a product such as RowaPhos can come into play. At certain points (say when IP first enters the tank, or it is unbound by bacteria and not used or not needed as their population is in a state of flux) RP can act as an absorbant to remove it. So....just one small part of the over all battle against Phophate saturation.
So anyway if I havent muddied up the water to much perhaps we can talk about it.
Mojo
Honestly didn't realize there were so many angles to phosphates. I think alot of the time people are so concerned about nitrate levels that they tend to forget they have phosphates to deal with as well which we see comes in so many forms. One good thing though is that some methods for limiting nitrates works hand in hand with limiting phosphates as well like using a macroalgae for nutrient export, water changes using ro/di water etc. 
