Hi all,
I a discussion over on a reef forum about GFO, Granular FerricOxide, phosphate binding media a few people pointed out that the GFOs dont bind the fosfate they only store it in an equilibrium state with the surrounding water.

As Randy-Holmes Farley explains:

So, if I where to take a high concentration solution of phosphate and dip the GFO media in until it's saturated and the place it in a planted tank the GFO media would slowly release fosfate into the water column. I am sure that calculations can be made to achieve a specific level of fostfate.

This has quite a few possibilites, dosing PO4 once a week or month even, the GFO will absorb the dosed PO4 and release it slowly into the water column. Gone are the need for dosing pumps and physics will do the job. We can maintain an exact level of PO4, even without measuring, for longer periods of time.

I havent found an equilibrium based NO3 binding media yet but I'm sure there has to be one. If there is one for NO3 and one for K I'd say binding media could be utilised as a complete regimen for dosing macro.

What do you all think?
cheers
Mattias

Yea, we call it clay and soil.

GFO, agar like materials etc, slow time release osmocoat fertilizers etc.
This idea is far from new.

PO4 and Fe etc bind to each other and they can also be acidified/reduced to break that bond and into the soluble phase.

Then they can be attached to a binding agent, say clay. The PO4 will bind to the iron fraction and the Fe to the negtaive charged clay particles.
Organic soil matter will do the same type of thing.

Root tabs/substrates can/do use these slower time release methods.
Dosing pumps can do the same thing.

So we can add these to the substrate where most folks using such materials generally do, I guess in marine systems, that's a novel idea or something

Well, Miracle Mud, but that's mainly for the reducing power to solublize the metals at the high pH's in the substrate DBS's.

The amount that gets into the water column is small, and variable and very hard to detect if not impossible for an aquarist certainly. We could use radiolabels Fe, PO4 etc to how much goes through ina pulse chase experiment or use stable isotope enrichment etc.

But those are not methods used by aquarist by any means.

Note, Iron is/was often added to in lake management for PO4 precipitation to control algae and aquatic weeds. The Fe locks the PO4 up into the sediment this way and makes the PO4 no longer in the bioavailable phase.

This idea is very old.



Regards,
Tom Barr

Ok,
so you mean there are clays and soils that can act as a phosphate buffering system? I.e. absorb when leves are high and release when levels are low. Or, are you just taking about ways of dosing?
//Mattias

These are sediments that come in contract with the water column.

As the level of reduction goes down to more negative values, say 100 mv's, the FePO4 bond is now broken and relases the Fe and PO4 into the aerobic water column, some will be oxidized and fall out of solution back to the sediment again.

Some will make it to plants, and algae.
Search for CEC of soils for more.
clays have a lot of CEC's, they can bind metals etc and then release them later under the presence of plant roots or reductive conditions.



Regards,
Tom Barr