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