Alk consumption

What else does iron oxide hydroxide bind? Metals

These materials are known to bind a wide range of other compounds from water, including trace metals, arsenic, selenium,2 silicate, and organics. Metals such as manganese, cobalt, nickel, and zinc are known to bind to iron oxide hydroxide in simulated seawater solutions.4,5 It has also been claimed that the binding of copper and zinc by natural iron oxide hydroxide sediments exerts a powerful control on the concentration of copper and zinc in polluted rivers and estuaries.6 Although not studied in seawater, it has also been observed that phosphate binding by iron oxide hydroxide actually increases its binding of copper, cadmium, and nickel in freshwater.7

Whether the binding of any of these ions is important in aquaria, and whether it should be considered a benefit or a detriment, remains to be established for each trace metal. Nevertheless, it is something that aquarists should keep in mind, and it may also be important in suggesting potential explanations for some of the biological effects of using these materials that are discussed later in this article.

What else does iron oxide hydroxide bind? Organics

Granular ferric oxide is also known to bind organic materials.8-10 In addition to many studies on the binding of man-made chemicals8 and natural organics from freshwater (such as humic acids),9 it has also been demonstrated that dissolved organic phosphate is readily removed from seawater by binding it to iron hydroxide.10

The binding of organics, especially those containing phosphorus, is likely to be beneficial in most aquarium circumstances. One possible exception is during treatments of the aquarium with organic medications. How effective this binding is compared to activated carbon, or whether they even bind the same materials, is unknown. It would be expected, however, that certain very polar organic materials might well be bound by GFO, and not by carbon. These would include certain natural biochemicals that might readily provide phosphate to algae, but that are too polar to be absorbed by activated carbon.

It should also be noted that GFO would not be expected to be very effective at binding purely hydrophobic molecules that will bind well to activated carbon. Consequently, GFO and carbon are in some ways complimentary in their ability to bind organic materials. If I had to select between the two for removing dissolved organics from aquaria, I'd select activated carbon.

What else might iron oxide hydroxide do? Precipitation of CaCO3

Many aquarists using GFO have reported unusually extensive precipitation of carbonates on the solid GFO, and elsewhere in the system. Such precipitation can, for example, be a contributing factor in the caking of such materials, and can coat other surfaces in the aquarium. This precipitation can also contribute to a drop in alkalinity and possibly pH as it removes carbonate from the water column. The effect of calcium will be similar, but smaller on a percentage basis, with a drop of only 20 ppm calcium for every 1 meq/L (2.8 dkH) drop in alkalinity. Increased calcification by corals and coralline algae (possibly spurred by reduced phosphate) can also cause similar drops in calcium, alkalinity, and pH.

Dissolution of these precipitates with acid, accompanied by bubbling, indicates that these deposits are carbonates, and are most likely calcium carbonate since it is supersaturated in most reef aquaria (and in the ocean). Several factors may contribute to this precipitation. Many of these are rather straightforward. It is known, for example, that phosphate inhibits the precipitation of calcium carbonate. Much like the role that magnesium plays in seawater, phosphate binds to the growing calcium carbonate crystals, poisoning their surface against further precipitation of calcium carbonate. Many organic materials are also known to inhibit this precipitation. Near the surface of the GFO, and downstream from it, the organics and phosphate are expected to be lower in concentration than upstream from it. The reduction in concentration of these inhibitors may well permit increased abiotic precipitation of calcium carbonate on such surfaces.

Two more esoteric events may, however, be equally important. The first is that the local pH near the GFO surfaces may be higher than in the bulk solution. This effect arises as phosphate and other inorganic and organic ions displace hydroxide from the surface. Figure 2, for example, shows phosphate displacing two hydroxide ions. The net swap of HPO4-- for 2 OH- will raise the local pH. The supersaturation of calcium carbonate increases as the pH rises, driving the precipitation of calcium carbonate.

Another possible role may be played by the iron itself. GFO is not completely insoluble. The solubility of iron hydroxide in natural seawater is small, but still significant (0.02 - 2 ppb), although it is largely controlled by the availability of organic ligands.11-13 One interesting possibility lies in the way that soluble iron actually impacts the precipitation of calcium carbonate.

At high concentrations, iron inhibits the precipitation of calcium carbonate. While different researchers find different threshold concentrations for this inhibition (>25 ppm in one case,14>7ppm in another case15), it is a well established and studied phenomenon. The mechanism is believed to be the same as for magnesium, phosphate, and organics, which all poison the growing calcium carbonate surface.

At much lower concentrations, however, iron actually increases the precipitation of calcium carbonate by acting as a site for nucleation of new crystals. In one case this happened at 100 ppb dissolved iron, increasing the rate of scaling (the precipitation of calcium carbonate on surfaces) by about 60%.14 In another case, the induction time for precipitation (that is, the time it takes for precipitation to begin once the water becomes supersaturated) was reduced by 40% at 1.4 ppm iron and the overall precipitation rate was increased by 32% at 560 ppb (lower iron levels were not tested).15 These studies were carried out in freshwater, and I have not seen similar studies in seawater.

Is the natural dissolution of GFO important in the nucleation of calcium carbonate precipitation? I am not sure. But it is clearly one possible explanation that fits the observations of aquarists as well as known phenomena involving iron.

What else might iron oxide hydroxide do? Biological effects

Quite a large proportion of aquarists using GFO in reef aquaria have reported undesirable effects on corals. These reported effects include tissue recession and bleaching. Many advanced aquarists have associated these effects with the first addition, or with a later change, of the GFO. While many or all of these reports may be coincidence, there are enough reports that aquarists should be wary. Listed below are a number of possibilities that may be the cause:
1.
A sudden drop in phosphate may stress certain organisms. This stress might be particularly important to corals with algal symbionts. The level of symbionts existing in a coral may depend to some extent on the availability of nutrients. A sudden drop in nutrients may imbalance the organism, leaving it with too many zooxanthellae for the newly-reduced nutrient levels. Especially if these corals are already living on the edge of survival, such stress may tip the balance toward disease.

2.
In some cases, phosphate levels may drop below natural seawater levels, and phosphate may become the limiting nutrient. If this limitation is severe enough, corals and other organisms using phosphate may well be stressed, stop growing, and become more susceptible to disease.

3.
Similar effects may result from a drop in certain trace metals. Since the effects of GFO on trace elements have not been clearly established in aquaria, it is possible that one or more critical elements may drop below optimal levels.

4.
The release of soluble iron hydroxide itself may irritate certain corals, although many aquarists dose chelated iron without such effects. The iron hydroxide may, however, nucleate the precipitation of calcium carbonate in sub-optimal places, such as tissue surfaces. It may also bind directly to tissues.

5.
The GFO may actually release certain metals other than iron from its surface. I have not seen any data on the chemical purity of these materials, and such issues may be a concern with some or all brands.

6.
The drop in alkalinity and/or pH caused by abiotic precipitation of calcium carbonate would not be expected to be very great in most aquaria, and typically isn't especially large, as reported by the aquarists themselves. In the cases from which I've seen data, the effect is not as great as the variability between aquaria or between dosing events in many aquaria. Still, such changes might be important in some circumstances where conditions are already marginal.

7.
Since GFO binds organic materials, the addition of a significant amount of fresh surface area may rapidly drop the dissolved organic levels. Such a drop may stress corals by rapidly increasing the available light levels, or by reducing a food source, or both.In order to minimize such difficulties, many aquarists start off using GFO more slowly than the directions might suggest. Such caution seems warranted in most cases.

I replace my GFO and most of my GAC every two weeks.
I don't keep track of phosphate. Years ago when I last measured it, it was often around 0.03 ppm.

I grow Caulerpa racemosa as it has outcompeted the Chaetomorpha in my tank, so I conclude it is more efficient at nutrient export.

Randy, if you don't test phosphate when do you replace the gfo? I keep my reactor running probably long after the gfo is exhausted, but I only change it when my phosphates creep above 0.03 (hanna ultra low). Seems expensive to swap it out on a regular basis if it's not reached capacity.

Guesswork, combined with laziness. It is likely always depleted before I get to it. How long between glass scrapings are needed is a potential indication, but mine usually needs it in 24-48 h regardless of new vs old GFO.

That's an advantage of having many different phosphate export methods as I do since when one stops (like GFO being depleted), the others are still functioning and may take up at least some of the slack.

You didn't say how long before you took a measurement. I thought it might have been a few days, in which time it could easily be depleted, and if you have truly elevated phosphate (and the reactor is actually exposing water well to the GFO), then adding more and changing it more often can be a good idea.

I use many nutrient export methods at once. I use GFO, GAC, skimming, organic carbon dosing (vinegar), and three large refugia filled with live rock and topped with macroalgae

The higher the phosphate in the water, the more phosphate will bind to such materials. The binding is reversible, so whether it is full or not, if it has reached an equilibrium with a higher phosphate level and is then exposed to a lower phosphate level, some phosphate will come off until it reaches a new equilibrium. The pH also has an effect, although I'm not sure what the pH profile looks like for GFO/phosphate.

It is also quite possible that with various ions competing for GFO binding sites (phosphate, silicate, organics, etc) that even if an ion is bound, something that comes along that binds more strongly may "bump it off".

Above are all excerpts and or Quotes from Randy. One thing that throws me is I'm going to use one product to have to replenish other products because of the first produce I added depleted them ? Sounds Costly and time consuming. Second Randy uses many different phosphate export methods in his tank including GFO, plant, and vodka dosing.
Randy states many times in many articles that GFO can be exhausted in DAYS, and also sates that GFO can maintain an equilibrium in removal and leaching. This means you can have a reading of .03 in your tank do a water change and the GFO can leach Phosphates back into your tank until the equilibrium point is reached. This also means that your tank can have phosphates at .03ppm for days or weeks, and maintain that reading, it will not go down. When the Phosphates starts rising and do not go back down then it is exhausted.

If you dig there is also some controversy about the mount of iron that is being put into a tank using GFO. Iron is a great fertilizer for Macro algae but also for micro algae and in some circumstances has caused algae bloom problems.


Randy states he has to clean his glass of Algae every 24 to 48 hours regardless, if it's on his glass at that rate it is elsewhere in his tank as well. I clean my glass once every two or three weeks. So obviously something is not working.


I'll pass on the GFO as well, too much back and forth screwing with the water chemistry.

If it works for you, Great, good luck with it.

I just love this. Randy how do you know when your GFO is exhausted? Guesswork, combined with laziness. It is likely always depleted before I get to it. How long between glass scrapings are needed is a potential indication, but mine usually needs it in 24-48 h regardless of new vs old GFO.

Instead of getting on the defensive and mis quoting what I said in the past. I just posted quotes from Randy to show what he is saying . Don't shot the messenger.
 
1. Do some research  iron (FE) is a metal and dissolves when in water especially salt water and Randy states that they use it to get Macro algae to grow faster and out compete Micro algae and starve off the Micro algae. He also states that in some instances Aquarist have suffered algae blooms. It has been proven that when you put media into a reactor and have it tumbling the particles DO break down, even though you have that sponge on top some particulate does get into your tank.

2. Hmmm how do you know it is your rock? could it be your sand, could it be the food your are feeding? Some foods are known to have phosphates in excess of .04+

3. Cleaning your glass once a week so you are getting brown algae on your glass and need to clean it once a week, I don't know what good or bad of a gauge that is. Again, I was quoting a scientific way Randy Gauges when his GFO is exhausted. I clean my glass once every three or so weeks.

4. If it is not detrimental what or how much metals GFO absorbs then you should not be adding any other additives to your tank and you should not care about the amount or the reading salt mixes have. Randy was part of a few scientist that performed test on Salt to see the best and they elected the best based on the ones that had the highest additive readings. My point on this is you are spending a boat load on the GFO which in turn takes the metals out of your systems water and in turn you spend more money on more additives.

5. Again reading too  much confusing posts and rehashing information. I ran a test in two separate 10 gallon tanks with lanthanum chloride. I never ran lanthanum chloride in my main tank as I didn't and still don't have the balls to.

The moral of this story is that many aquarist and scientist have run test on bringing down phoshates quickly and it is not a good thing ever, most of the time with tank crashes and corals bleaching. Macro algae does remove phosphates slowly but are a good rate st to not shock your tank. The problem is that you need a good amount of macro algae to work. Again Randy uses four or five processes to remove phosphates, including a huge amount of algae.
I have experimented with GFO in the past and it did nothing for my but produce a case of brown algae that I could not get rid of until I stopped GFO."
I believe the moral of the story is that you shouldn't tell people things don't work when they do." So why do you do it      "Different systems requier different things" So you are saying some things work for one tank when they don't work for others? This may be the best statement you have made on here.
 Syntax sorry for stealing your thread.  

As stated before GFO is known to drop Alk and also if algae whether coralline, macro, or micro is starting to take hold this could cause an Alk drop.