Does GFO leach iron?

[ROR]

Does granular ferric oxide leach iron into the water? I'm wondering if I'm running a Phosban reactor do I need to still dose iron for macro growth, or at least should I reduce the dose. Is it possible to OD iron by doing both?

Rob

[m2434]

I think it is fairly safe to say iron hydroxide will be released. However, I don't believe this is biologicaly useable and would probably precipitate anyway. But I'm currious as to whether anyone else has any insight...

[bertoni]

I agree that some iron likely is going to make it into the water column. As long as the media is not being abraded, though, I think GFO media are fine to use. I doubt that backing off on the iron supplement is necessary.

[Randy Holmes-Farley]

I think it remains an open question whether enough soluble iron is released or not. Wild guess, I'd say yes.

[bertoni]

Thanks, Randy!

[ROR]

Thanks!
The reason I asked is because I've been getting some extra brown algae growth since starting a Phosban reactor (strange, I know). Took me a while, but it finally dawned on me that perhaps this was caused by too much iron in my system. I'm going to cut out the iron supplement and see what happens.

Rob

[SimilanRocks]

I have similar experience witht the GFO. The instruction says I don't need to wash it. It created iron cloud that precipitate quickly to the bottom of the sump. Next day I saw a lot of cyano on where the iron was.

I'm wondering what caused the cyano. The iron itself, or the phosphate/silicate that binded to the iron?

[bigtex52]

Now that you mention it, I am having the same probs! Started running GFO last weekend and suddenly the cyano is going wild on my rock. It blows off easy enough with a baster but still looks like heck.

[bertoni]

I can't guess as to why there's a cyanobacterial outbreak in these cases. Maybe it's iron, or perhaps there's some change in the ecosystem due to the change in the balance of nutrients. I don't think that GFO products are likely to release phosphate or silica very easily.

[m2434]

Usually I run GFO if I have nuisance algae. After the GFO, cyano is the only one remaining, but it's grow does seem very limited I had assumed that compared to other algae it isn't particularly P limited, but it would be interesting if there was something else going on as well.

[acrylic_300]

Any chance that the cyano are more adept at living without phosphate than other bacteria that compete with them?

[bertoni]

Cyanobacteria might be favored in various conditions, but I have no idea what might help or hurt.

[TekCat]

Don't mean to steal the tread...
I have the same issue, GFO is in use but cyano doesn't go away. My nitrates rather high (25ppm), so since C-N-P balance is messed up due to low P and high N, I guess vodka method wont work. Any suggestion to battle N?

[bertoni]

That's interesting. Apparently, the cyanobacteria can outcompete the GFO for phosphate. What media is being used, and how much?

[TekCat]

I use phosar hc... about half of a can in a 90+30g system.

[m2434]

Most cyano will produce (fix) nitrogen from N2 rather than consume it. I've found some good articles related to this topic, but I haven't had a chance to read through them more thoroughly. A preliminary scan of these articles suggests iron may be more limitting for cyano than other bacteria/algae. So, I could be on to something, but I'm not sure.Unfortunately I will be away most of the day, but hopefully I'll get caught up on my reading early next week.

In the meantime, if you are intrested in more detailed info try searching google scholar with keywords phophate, iron, limitation (hint: particularly look at the cyanobacterium Trichodesmium)

[bertoni]

Really? I didn't think that cyanobacteria were so inclined to fix nitrogen. That sounds energy-intensive in an environment with plenty of nitrate.

[m2434]

Whoops - should say "under the right conditions most cyano will produce (fix) nitrogen from N2 rather than consume it".

Sorry...

[ROR]

Hmmm... My system is low nutrient, I always register 0 for nitrates with a test kit (for what it's worth), but since starting GFO I've also had some persistent patches of Cyano. Perhaps iron somehow aids Cyano in fixing nitrate.

I've just done a 2 day total system blackout. After 2 days of having the lights back on again with no iron dosing I have no Cyano yet.

[m2434]

Originally posted by ROR
Hmmm... My system is low nutrient, I always register 0 for nitrates with a test kit (for what it's worth), but since starting GFO I've also had some persistent patches of Cyano. Perhaps iron somehow aids Cyano in fixing nitrate.

I've just done a 2 day total system blackout. After 2 days of having the lights back on again with no iron dosing I have no Cyano yet.

Someone correct me if I'm wrong, but I believe cyano has mechanisms to utilize forms of iron that would not typically be biologicaly available. If it could utilize iron hydroxide, for example, then might it also utilize an attached phosphate group?

As to nitrogen fixation, logically, it would only fix N2 if inorganic N was low.
However, I'm not sure this is always true. However, its not entirely clear to me under which conditions cyano does fix N2 either.

[Randy Holmes-Farley]

Cyano are very good at scavenging iron by releasing organic compounds into the water that bind iron, called siderophores, and then these are taken back up into the cyano as an iron source.

Whether that is because they have a specially high need for iron, or whether they are adapting to surviving in especially low iron environments is not clear, but they may well be able to get iron from insoluble iron oxide/hydroxide when other species cannot.

In general, I don't think we want any tank organisms to be iron deficient, but if somehow using a lot of iron in some form promotes cyano over other species, that is worth understanding and potentially dealing with, perhaps by not using iron in cyano problem tanks and seeing if that helps.

This article has more:

Second Iron Article: Iron: A Look at Organisms Other than Macroalgae
http://www.advancedaquarist.com/issues/oct2002/chem.htm


from it:

"Cyanobacteria and Iron

It has been suggested by some hobbyists that iron additions to reef tanks may drive the growth of cyanobacteria, and that one should not dose it for that reason. I’ve not seen that effect in my tank, nor have I heard it reported in others. It was also not reported to be significant in the open ocean studies described above. Nevertheless, since cyanobacteria are a problem for many reefkeepers, this issue is an especially important one to address.

Fortunately, there is a great deal of literature on the relationship between iron and cyanobacteria. Most of the literature indicates that cyanobacteria are especially well suited to low iron environments because they are able to release siderophores that bind to iron and give them a competitive advantage over other organisms. This is, in fact, one of the reasons why they have been studied so extensively with respect to iron. If they do generally have a competitive edge at low iron levels, then adding iron supplements and swamping out this competitive advantage may make strategic sense if reducing cyanobacteria is a goal.

In one paper, for example, the researchers conclude “that cyanobacteria are efficiently adapted to grow in low-Fe environments (providing sufficient light for photosynthesis is available)…” 15 In a different paper, the researchers state: “This review focuses on how cyanobacteria respond to growth-limiting levels of available iron and on how siderophores potentially alter the biological availability of iron in the system thereby allowing the cyanobacteria to exist at low iron availabilities.” 16 In another paper the researchers show that “The growth rates and intracellular and total cellular
iron levels for Synechococcus PCC 7002 demonstrate that iron availability does not directly dictate the maximum growth rate of these cyanobacteria…”17

Finally, in this paper, it appears that the three species of cyanobacteria tested are not iron limited for growth in the ocean (2 are phosphate limited, the other may be phosphate limited) while one of the species of macroalgae may be iron limited (Dictyota bartayresiana). 18

To be fair, some researchers do make seemingly contrary claims, though the fact that there are many species of cyanobacteria makes that result not overly surprising. One research group states that “Our results suggest that in 75% of the global ocean, iron availability limits nitrogen fixation by this organism.”19 Previously, other researchers had shown that iron does indeed stimulate growth of this particular cyanobacterium.20

These results for cyanobacteria are essentially what one would expect for an organism that can grow well even in low iron conditions. This fact does not demonstrate that the cyanobacteria won’t become iron limited under the higher phosphate and nitrate conditions present in a reef tank, but it also does not indicate that there is, at present, any cause for alarm about cyanobacteria and iron additions."

[SimilanRocks]

Originally posted by Randy Holmes-Farley

Finally, in this paper, it appears that the three species of cyanobacteria tested are not iron limited for growth in the ocean (2 are phosphate limited, the other may be phosphate limited) while one of the species of macroalgae may be iron limited (Dictyota bartayresiana). 18

So if we use GFO to limit the phosphate, we should see less cyano problem, even if the GFO is leaching iron?

In high phosphate tank adding GFO can create cyano bloom, over time GFO should outperform cyano?

[tmz]

Originally posted by m2434
Whoops - should say "under the right conditions most cyano will produce (fix) nitrogen from N2 rather than consume it".

Sorry...

As I understand it cyanobacteria use CO2 water and light to produce sugar and oxygen as do other autotrophs. Then they uniquely grow anoxic sacks in their structure where an element which would not work in an oxic environment called nitorgenase uses atmospheric oxygen to create biologically useble compunds such as ammonia, nitrite and nitrate. I do not think cyano uses phosphate which may explain why it grows when gfo is used since perhaps the lack of phosphate is limiting to nuisance algae but not cyanobacteria.

[tmz]

Sorry. I meant to say significant phosphate, but if they are phosphate limited as noted then the question would be at what level of phosphate as compared to the algae.

[m2434]

I'm finding hints that suggest cyano may outcompete algae for limited phosphate. Also, cyanobacteria may be able to store phosphate well, so removing the source may not stave them, but they probably wouldn't grow either.

So over time, GFO should out compete cyano - if you can remove whats there.

The only possibl eexeption I can think of, at the moment, goes back to the iron issue. I'm not sure about this, but if siderophores bind insoluble iron, what happens to any phosphate attached to that iron. If it's freed then this could provide an additional food source for cyano, but I'm not sure.

Generally however, I think it's safe to say there are numerous reasons why cyano may survive.

I'm fairly sure about the following statements (ordered by my confidence in them from most confidence to slightlty less):

1) Not much eats it.
2) It's not really limited by inorganic nitrogen, because it can fix it.
3) It can utilize insoluble forms of iron.
4) Can store phosphates well
5) Can rapidly compete for remaining phosphate.