I wonder to what extent the iron oxide (rust) is used for in removing phosphates. I was just researching types of rock and had read about iron oxide and how it isn't reactionary in water and is not metabolized by fish. Maybe it's not the actual phosphate remover but simply a part of the make up?
Sent from my iPhone using Tapatalk
I really have no idea whatsoever, I'm thinking more about the aluminum but really curious on this. I just re read and its iron oxide hydroxide if that makes a difference. Also different phosphates apparently may or may not be affected. So is it possible the phosphates we dose are not affected and other organic phosphates are affected? I'm so lost on this issue.
I'm going to copy/paste the relevant info below.... fair warning its long.
This is the relevant info from the source I linked. Any chemists here?
Phosphate Export Using Binding Media: Aluminum Oxide
Aluminum oxide is the primary ingredient in several commercial phosphate binders, such as Seachem's PhosGuard™. These materials are always white solids, although not all white phosphate binders are aluminum oxide. Phosphate binds strongly to aluminum ions exposed on the surface of aluminum oxide solids. Phosphate is believed to bind to aluminum-containing surfaces through a direct ionic interaction between one or two negatively charged oxygen ions on the phosphate with the aluminum ions (Al+++) exposed on the solid surface. After exposure to the aquarium water for sufficient time to adsorb phosphate, the solids are removed and the phosphate is removed along with it. This process has been used historically in other industries as well, including phosphate binding in people, where aluminum use is no longer recommended due to toxicity concerns.
Unfortunately, aluminum oxide is not completely insoluble in seawater. I have shown experimentally that aluminum can be released from PhosGuard™, and I have also shown that adding the same amount of released aluminum back into an aquarium can irritate corals, causing them to retract their polyps and otherwise shrink. That effect mirrors what many aquarists reported (prior to this test) as a side effect of using these media. Rinsing the solids before use can reduce the likelihood that small aluminum-containing particulates are released into the aquarium, but it does not prevent the solubilization of aluminum ions from the solid surfaces.
That all said, many people use aluminum oxide effectively, and many never notice any negative effects. I have used it in the past without noticing harm in my aquarium, although I have used only small amounts. Rinsing it before use and not using large amounts all at once will limit any negative impact.
Phosphate Export Using Binding Media: Granular Ferric Oxide/Hydroxide
In the past few years iron-based phosphate binding materials have become very popular among reef aquarists. These materials have been used commercially to treat drinking water (to remove arsenic, for example) and to treat wastewater (to remove a wide range of pollutants, including phosphate). They are sold to aquarists under a variety of different brand names, including PhosBan®, Phosphate Killer™, and ROWA®phos. These materials all range in color from reddish brown to nearly black. In a previous article I detailed how they function as well as some of the concerns that aquarists have had when using this material.
Even though the commercial materials appear to be reasonably large particles (Salifert claims 0.2 - 2 mm on its product label), they actually have a high internal surface area, somewhat similar to activated carbon. Consequently, apparent particle size is an unreliable means by which to gauge available surface area (though it is reliable for nonporous solids such as table salt). I have seen no measures of accessible surface area for the commercial granular ferric oxide (GFO) sold to aquarists. Warner Marine has recently released a type of GFO (called PHOSaR) that has larger particles than most other brands of GFO, making it potentially more amenable to use in a typical media bag without as much concern for releasing fine particulates to the aquarium. I've not tested it myself.
Phosphate bound to GFO surfaces is still available to the water column by exchange, so the sequestering is temporary rather than permanent. This fact is known in the literature3, and can be shown experimentally. I will show the detail in upcoming articles, but it can easily be demonstrated by adsorbing phosphate onto GFO, and adding enough so that a detectable concentration of phosphate (say, 0.1 to 1 ppm) is in equilibrium with the solids. Then remove the solid GFO and add it to seawater with no detectable phosphate. The now-detectable phosphate in the new seawater shows that the phosphate can be released from the GFO media when the aquarium's phosphate concentration drops low enough.
One concern when using GFO is that it may add soluble iron to the system. This iron will likely benefit growing macroalgae, and I recommend adding soluble iron to systems that grow macroalgae. However, low bioavailability of iron may limit undesirable algae growth in some aquaria (it can in parts of the ocean), so adding iron might contribute to an algae problem. In general, however, most aquarists find that the use of GFO causes a decline in algae, with the reduction in phosphate being more important to decreasing algae growth than the added iron is to promoting it.
A second concern with using GFO is that some aquarists find extensive precipitation of calcium carbonate near or on the GFO itself. It turns out that soluble iron can cause the precipitation of calcium carbonate. Such precipitation can turn bags of GFO into solid clumps, and may contribute to clogging pumps, but in general the effect, if noticed at all, is limited to objects very near the GFO. The extent of this effect may well depend on the degree to which calcium carbonate is supersaturated in the aquarium, as well as on the levels of magnesium and organics (both of which usually reduce the likelihood of calcium carbonate precipitation).
Finally, be sure to rinse these materials in fresh or saltwater before adding them to the aquarium, as fine particles may get loose in the aquarium, clouding and coloring the water, and possibly creating other problems. There is no efficiency drawback to this rinsing. Aquarists using the GFO in a fluidized bed reactor or canister filter can just run some fresh or salt water on it for a few minutes before putting it into the aquarium. A media bag of GFO can simply be rinsed with saltwater or RO/DI water a few times before adding it to the aquarium. Do not squeeze the GFO inside the bag when rinsing it, as that may break the particles into smaller bits that can escape the bag.
The bottom line: Would I use GFO to export phosphate? The answer is yes, and I often do so by adding some into a canister filter that also contains activated carbon.
Soluble metal salts can work to remove phosphates by precipitating insoluble phosphate salts. For example, carbonates and phosphates are added to water supplies to form a protective film on lead pipes. Flint had trouble when they changed the protective agent and the acidity change further reduced the effective concentration of their coating agent. That said, aluminum phosphate would not be a soluble form of aluminum ions. The chemistry of aluminum oxide is very stable. I am not sure of the conditions under which iron oxide will generate free iron ions in solution. As another aside, iron oxide can effectively remove other metals from solution. For example, iron oxide is very effective at removing trace arsenic. Some people make arsenic removing filters from rusty nails for rural areas in Bengledesh and other 2nd and 3rd world countries with arsenic problems.
My guess is that aluminum oxide is an inactive ingredient that serves a structural purpose. That said, I am not very familiar with these products.
I am chemical language challenged. So your thoughts would be that it would be unlikely to have any effect on phosphates in our aquariums when used in substrates such as BDBS?