Do phosphates really get absorbed by rocks and sand to be released at a later date to wreak havoc?

[Ram]

I was reading that phosphates might be absorbed by live rocks and sand to be released after you've removed all the phosphates from the water and can cause problems. Is this true and also does this apply to dry rock as well?

 

[Randy Holmes-Farley]

This poll can really only be applied to the "can cause problems" part of the question because it is a well established scientific fact that phosphate reversibly binds to calcium carbonate sand and rock surfaces.

Whether that is any problem depends, or course, on the specific system and how it deals with phosphate.

Here's a typical paper:

http://www.aoml.noaa.gov/flbay/millero1.html


Adsorption of Phosphate on Calcium Carbonate

Frank J. Millero, University of Miami/RSMAS, Miami, FL; Jia-Zhong Zhang, NOAA/AOML/OCD, Miami, FL

Phosphate, as a limiting nutrient, is critical to the onset and sustainment of phytoplankton blooms in Florida Bay. The adsorption of phosphate on suspended biogenic calcium carbonates (aragonite and calcite) is believed to be an important mechanism for removal of phosphate in the natural waters. Understanding the transportation and transformation of phosphate in the environment is important to the water quality of Florida Bay.

Laboratory experiments on phosphate adsorption show that the adsorption of phosphate on calcite and aragonite is a fast process. Generally it takes about 5 minutes for the adsorbed phosphate concentration to reach a constant value. Aragonite offers more active surface and more active adsorptive sites than calcite. The capacity of adsorption on the aragonite is about 20 times higher than calcite based on moles of phosphate adsorpted on per gram of particle. Adsorption isotherms have been constructed based on the equilibrium experiments of phosphate adsorption on aragonite at pH of 8.0 in seawater over salinity range of 5-35 and temperature range of 5 - 45 oC at initial phosphate concentrations over a range of 2 to 60 m M. Both Langmuir and Freundlich adsorption models have been used to fit the experimental data. The results indicated the existence of different binding sites with a wide spectrum of binding energies on the calcium carbonate surface. At low adsorption densities, surface sites with highest energy are occupied first. For both aragonite and calcite, the adsorption capacity increased as the salinity of seawater decreased. The effect of salinity on the adsorption might be related to the competition of phosphate between particle surface and magnesium in seawater. These results show that calcium carbonate can act as a fast scavenger for phosphate in the water. Future works will be focused on the natural suspended matter collected in Florida Bay. The composition of suspended matter, adsorption and desorption characteristic and the effect of natural organic matters and iron oxide on the surface properties will be investigated using the suspended matter and sediments from Florida Bay.

 

[Ram]

This poll can really only be applied to the "can cause problems" part of the question because it is a well established scientific fact that phosphate reversibly binds to calcium carbonate sand and rock surfaces.

Whether that is any problem depends, or course, on the specific system and how it deals with phosphate.

Here's a typical paper:

http://www.aoml.noaa.gov/flbay/millero1.html


Adsorption of Phosphate on Calcium Carbonate

Frank J. Millero, University of Miami/RSMAS, Miami, FL; Jia-Zhong Zhang, NOAA/AOML/OCD, Miami, FL

Phosphate, as a limiting nutrient, is critical to the onset and sustainment of phytoplankton blooms in Florida Bay. The adsorption of phosphate on suspended biogenic calcium carbonates (aragonite and calcite) is believed to be an important mechanism for removal of phosphate in the natural waters. Understanding the transportation and transformation of phosphate in the environment is important to the water quality of Florida Bay.

Laboratory experiments on phosphate adsorption show that the adsorption of phosphate on calcite and aragonite is a fast process. Generally it takes about 5 minutes for the adsorbed phosphate concentration to reach a constant value. Aragonite offers more active surface and more active adsorptive sites than calcite. The capacity of adsorption on the aragonite is about 20 times higher than calcite based on moles of phosphate adsorpted on per gram of particle. Adsorption isotherms have been constructed based on the equilibrium experiments of phosphate adsorption on aragonite at pH of 8.0 in seawater over salinity range of 5-35 and temperature range of 5 - 45 oC at initial phosphate concentrations over a range of 2 to 60 m M. Both Langmuir and Freundlich adsorption models have been used to fit the experimental data. The results indicated the existence of different binding sites with a wide spectrum of binding energies on the calcium carbonate surface. At low adsorption densities, surface sites with highest energy are occupied first. For both aragonite and calcite, the adsorption capacity increased as the salinity of seawater decreased. The effect of salinity on the adsorption might be related to the competition of phosphate between particle surface and magnesium in seawater. These results show that calcium carbonate can act as a fast scavenger for phosphate in the water. Future works will be focused on the natural suspended matter collected in Florida Bay. The composition of suspended matter, adsorption and desorption characteristic and the effect of natural organic matters and iron oxide on the surface properties will be investigated using the suspended matter and sediments from Florida Bay.

Great response! thanks. If I may add a question though. Once the phosphate has been absorbed by the calcium carbonates how can we remove the suspended calcium or is it safe to leave in the water at this point. Also Im assuming we can use kalkwasser to absorb the calcium am I correct? And, how long should this process take? do you recommend better ways to remove the phosphate. Again, thanks for your expertise.

 

[Randy Holmes-Farley]

The calcium carbonate it binds to are solids, like rock and sand. Not things dissolved in the water (unless you added some super fine sand that hasn't settled yet).

This binding is why a 100% water changes will not drop phosphate to zero while it can with nitrate. The bound phosphate acts as a reservoir that comes off when the concentration of phosphate in the water declines and goes onto the rock and sand when the concentration in the water rises.

The process happens fast on a flat surface, but it takes substantial tie to work its way into or out of sand or rock pores.

There are many good ways to remove phosphate. I use several at once, and discuss them here:

Phosphate In The Reef Aquarium
https://www.reef2reef.com/blog/phosphate-in-the-reef-aquarium-by-randy-holmes-farley/

 

[gettaReef]

The calcium carbonate it binds to are solids, like rock and sand. Not things dissolved in the water (unless you added some super fine sand that hasn't settled yet).

This binding is why a 100% water changes will not drop phosphate to zero while it can with nitrate. The bound phosphate acts as a reservoir that comes off when the concentration of phosphate in the water declines and goes onto the rock and sand when the concentration in the water rises.

The process happens fast on a flat surface, but it takes substantial tie to work its way into or out of sand or rock pores.

There are many good ways to remove phosphate. I use several a tonce, and discuss them here:

Phosphate In The Reef Aquarium
https://www.reef2reef.com/blog/?p=3184

Your link took me to the thread "OT survey - Music" lol

 

[Randy Holmes-Farley]

Huh. It works for me, but try this and I'll replace the link above too:

https://www.reef2reef.com/blog/phosphate-in-the-reef-aquarium-by-randy-holmes-farley/

 

[Sabellafella]

What your seein on the forums is peoples rocks leach phosphates because they use dry pukani and dont take the time out to acid wash and pulani imo takr about 8 months to even cure