phosphorus storage

[charles matthews]

Randy,

Forgive me if you've covered this somewhere. I was curious about the limits of a sand bed's ability to store phosphorus. There is certainly a limit to organic storge. What about inorganic storage, such as precipitates on calcium carbonate? Also, would the addition of iron to a tank provide a route for phosphate storage via iron-phosphorus insoluble compounds?

Thanks as always

Charles

[Randy Holmes-Farley]

Caclium carbonate can bind a certain amount of phosphate on its surface as phosphate salts, just like the various commercial materials like GFO and aluminum oxide bind phosphate. The amount bound in that way is purely a function of the surface area and the phosphate concentration.

Phosphorus can also be held in organics, and inside of bacteria. There may also be precipitation of phosphate into calcium carbonate if it is accreting, and as pure calcium phosphate.

Whether any of these in the second paragraph are significant to a reef aquarium is, IMO, undemonstrated, although that doesn't mean it isn't important.

I do not know if adding any iron supplements or GFO to a reef aquarium impacts phosphate cycling on the substrate, but it might.

I discuss iron in more detail in these articles:

Iron Oxide Hydroxide (GFO) Phosphate Binders
http://reefkeeping.com/issues/2004-11/rhf/index.htm


First Iron Article: Macroalgae and Dosing Recommendations
http://www.advancedaquarist.com/issues/aug2002/chem.htm

Second Iron Article: Iron: A Look at Organisms Other than Macroalgae
http://www.advancedaquarist.com/issues/oct2002/chem.htm

[charles matthews]

Thanks, Randy. So, it sounds like you are saying that sand beds have a maximum ability to store phosphorus- after which that capacity is exhausted- except perhaps if iron additions may increase that capacity?

[Randy Holmes-Farley]

Some of the processes have a maximum capacity, yes. I've never thought of sand or live rock as a significant permanent sink for phosphate.