Convinced of a link between GFO and Cyano (and not the good kind)
 

After my massive renovation related coral losses, I've been doing everything I can to get the tank back on track. Part and parcel of that has been to amp up the GFO use as, much to my dismay, the pump that drove my reactor died sometime while my house was being renovated in August. For at least a month, the tank had no GFO, in addition to no water changes.

While my corals were dying like it was the hottest new trend of 2014, the one problem my tank had absolutely none of was cyano. As some of you may remember from earlier posts of mine, I've been struggling with cyano for a while now, as it always seems to capitalize on dying coral and smothers the newly dead skeleton - sometimes within hours of the RTN event.

So anyway - I replumbed the the return pump assembly of my tank and replaced my external reeflo with one mother of an internal, quieter, more energy efficient pump and built a manifold off that line to run a new reactor that sits next to the sump where the old pump used to be. It took 3 days cuz I'm no plumber, but voila, no more making a giant wet mess every time I want to change the media, and no more bulky reactor and pump in my sump. I add a fresh batch of incredibly well rinsed Rowa phos and BOOM! Next day cyano shows up pretty much everywhere.

I kid you not - ZERO cyano in the tank the day before, even on coral skeleton that had been dead long enough to turn green and start to grow coraline. Day after adding GFO back to the system - traces of cyano on everything. Fast forward to today, and even with 400% cumulative total water change, insane attention to parameters, the removal of about 60% of the dead, exposed corals skeletons, and the cyano problem continues to worsen daily.

I have now read far too much literature on "black reefs - large swaths of pristine reefs that are smothered and die under a thick blanket of cyano bacteria - happening within months or years of iron hulled ships wrecking and sinking on them, to not be suspicious of the F in GFO as a possible driving culprit of cyano bacteria. The most recent research on black reefs seems to confirm that it is the sudden availability of excess iron from the rusting hulls that drives these systems towards cyanobacterial dominance. To make an even more convincing case, some very crazy (smart?) people have been suggesting dumping huge amounts of iron in to the open ocean specifically to cause massive algae blooms for carbon sequestration for a couple of years now.

When people get cyano, the standard wisdom is to ramp up your GFO use because clearly you must have a phosphate issue. But I can't count the number of threads I've seen where people do exactly that and their problem gets no better or just gets worse. I've also been able to find a bunch of threads around the internet where people have noted cyano appearing immediately after first additions of GFO. Suggestions are usually that somehow the cyano is now being favoured by a reduced nutrient environment, but almost never does anyone suggest that the significant amounts of iron hydroxide dust that gets dumped in to a tank with every GFO change might actually be as vital a nutrient to cyano (which uses a relatively large number of iron atoms in their photosynthetic structures compared to other autotrophs) as N, P and C.

I never had so much as a trace of cyano when I was using PO4x4, which encapsulates the GFO in some sort of polymer bead. Literally the first time I saw cyano in my tank was the same window of time that I stopped using that expensive and hard to get product and switched to a granulated, dust producing form. I've battled it ever since.

That was a long rant (but hey, I write long rants sometimes), but I'm now very seriously looking in to non-iron based phosphate adsorbers and if I can get over my fear of aluminum in a reef tank, I'll probably switch to see if it helps.

Does anyone know of other kinds of phosphate binders that can be used in a reef tank that aren't iron or aluminum based? Has anyone ever figured out how to use lanthanum chloride as a safe, routine (as in dosed in a daily and automated fashion) phosphate control method in a reef tank?

I use Foz Down in several systems and it is dosed via Profilux doser multiple times per day.

Both Wai's and Fiji Reef Rock have Foz Down available. This is what you are looking for.

Cheers,
Tim

I'm dosing diluted FozDown 12 times/day into a 10 micron sock via automated doser.
I've been dosing for about 1 month now and am now working on balancing the dosing amount to what I feed the tank.
My phosphate readings were about 60 ppb before and now they're consistently around 6 ppb. I'm checking the phosphate level weekly.

Very interesting. I haven't got my google on yet but where does the Fozdown deposit or send / store the phosphates?

The Foz Down binds with the Phosphate to create microscopic "snowflakes" called flocs. Some people choose to filter out the flocs using 10 micron filter socks while others let them settle out in the sump or tank.

Cheers,
Tim

What you're describing is common phenomena. The cyano bloom happens in our tanks from GFO for the same reasons it happens with biopellets - quick, significant lowering of phosphate. In other words, too much GFO (or too aggressive with biopellets). It can happen with Lanthanum chloride (FozDown) too for the same reason. It doesn't happen in every tank though under what appears to us to be similar circumstances which is obviously frustrating. Just as frustrating as high nutrient SPS tanks that get no waterchanges or dosing and grow SPS like weeds for years and years (lol). Anyway, the reason the cyano appears is because the water column is suddenly barren of phosphate yet the substrate and rock is still loaded. As the phosphate leeches out of the substrate and rock the cyano jumps in to feed off it as it leeches. Cyanobacteria are extremely efficient at processing phosphate.

The fix: Pull the GFO. Keep using carbon. Add a filter sock, then use a piece of rigid airline tubing with flexible airline tubing attached to make a mini siphon hose and suck the cyano out of the tank at the peak growth of the day (usually at peak lighting). Do this daily or every second day. After you suck out as much as possible use a turkey baster to blast every nook and cranny in the rock. Then use a feeding stick or the baster to stir up the top 1/2" of sand. Wait an hour and remove/change out the filter sock. It takes elbow grease, but it's very effective.

Next time, don't use so much GFO. 1 tbsp per 30 gallons changed out every 2-3 weeks is much "safer" than adding a whack and changing it out every 6-8 weeks.

Added note... in my experience, mature tanks shouldn't need GFO, and usually do better without it.

Right. The cyano will also appear on dying macro algae.
You'll still have to siphon the cyano out as it appears, if it does.

The key is keeping phosphate out of the water column in the long run. I'm finding it easier to dose Foz Down, it's a lot less hassle than GFO and I can instantly tweak the dosing to match my feeding schedule.

So is your filter sock just in the water or do you have flow of some sort running through it?

I have a CPR 4 inch sock holder mounted inside the sump with a maxijet 600 pumping sump water into it.
The dosing tube drips into the filter sock.

This is the common wisdom I'm suspicious of. There's never been any evidence or experimentation to show that this is true, it's just what people have surmised because they couldn't explain what they were seeing. But when you start to dissect it from a biological perspective, the notion that suddenly lowering phosphate levels would cause cyano bacteria doesn't make much sense.

1. If cyano is so good at taking up phosphate, it should do as fine a job pulling it out of the water column as it would out of the rocks. It wouldn't not grow when there was plenty available for cheap and easy in the water, then suddenly start growing when the easier to get at stuff disappeared. Chemicals diffuse along gradients, so cyano taking phosphate out solution directly above the rock it sits on top of will create micro gradients that phosphate can move across, regardless of the concentration in the water column. Further, there's good evidence to suggest cyano biofilms have multiple mechanisms that would allow them to actively harvest phosphate in the rocks they sit on top of (micro pH gradients, oxygen gradients, CO2 gradients, direct microbial weathering, etc), which is probably why it seems to favor recently exposed coral skeleton, as that stuff is loaded with phosphate. I can't think of a reason why reducing phosphate levels in the water column would enhance that activity that holds up to close scrutiny.

2. We like to think gfo reduces phosphate levels to "zero", but the truth is that even the most heavily gfo filtered tank water still has as much or more (usually MUCH more) dissolved phosphate in it as most wild reefs. On average it keeps it low, but phosphate levels moment to moment fluctuate in a tank (ie, right after feeding), even if the long term average is "low" due to gfo. If corals and coralline are growing, and you have to wipe your glass down ever, there's enough phosphate to support cyano, regardless of what your test kit tells you. I can also go on and give you reasons why hobby grade (and even some lab grade) phosphate test kits are pretty much never accurate within the range relevant to reef life, but that's another rant.

3. Cyano bacterial biofilms, which can achieve staggering amounts of surface area where 100% of the tanks volume flows over them every few minutes in the immediate vicinity of where phosphate (aka food) is added and broken down will almost certainly be better competitors for nutrients than a teeny tiny reactor in the sump, fed by a teeny tiny pump with flow throttled so the media barely bounces. Over time it brings down the phosphate level for sure and maintains it there on average, slowing the growth of algae, but that doesn't mean lots of other organisms don't have a chance to get some of it first.

Basically I'm saying I think that explanation has a lot of holes in it, and it's never been based on any evidence, or even a biologically reasonable theory. When you add a substance to an ecological system, and suddenly massive growth of a previously absent or minor organism occurs, the simplest (and therefore usually true) explanation is that that substance was a previously limiting nutrient for that organism.

We twist ourselves in knots trying to explain things we see in aquariums by invoking complicated "balance of the system" explanations that survive because they fit well within the narrative we tell ourselves about our tanks, and are virtually untestable.

The more simple answer is that even in a bio pellet or gfo treated tank, there was and always will be enough major nutrients like N and P for certain problem organisms like cyano grow, but that cyano can directly use the organic carbon or rust particles (or both) sloughed off in to the water column as food or an otherwise limiting nutrient.

In the case of gfo, there's plenty of scientific evidence to support the link between iron feeding cyano, but virtually no evidence to support the line of reasoning most aquarists have used to explain this sort of thing.

This is a great idea. I can run something similar off the manifold on my return line, and switch my gfo reactor to a carbon reactor.

Iron certainly does feed cyanobacteria (and pretty much any algae too), that's not a big discovery.

What I don't agree with is the iron being the trigger for the cyanobacteria. My opinion, based on my own experiences as well as hearing/reading talks by leading aquarists/biologists is that it is the imbalance of phosphate between the water column and the substrate that is the trigger. It's nearly impossible to keep cyanobacteria out of a reef tank, so it's the trigger for the explosion that you want to avoid. I've seen cyanobacteria in new tanks where old rock was used, and new saltwater was used. Also causing this imbalance. No GFO.

Cyanobacteria is certainly in the water column when it is on the substrate/rock. Think of the cyanobacteria clinging to the rocks like the fish swarming for the food. Most tanks have enough water movement so the cyano can't form clumps in the water column, but it certainly will if the water is not moving enough. In cases where there is a lot of cyano, I've often seen it floating in clumps in areas of low flow.

Keep in mind there are thousands of species of cyanobacteria.

Thanks. The sump water is also filtered first through a 200 micron sock from the display tank.

I'm not saying you can keep cyano out of a reef tank. But I am saying that the idea of an 'imbalance' as we tend to apply it to aquariums is a biologically meaningless term, and there's never been (that I've ever been able to find at least) any research in any kind of an analogous natural system that would support that idea. If it's an "imbalance", what would constitute a "balanced" state? There's always going to be phosphate in the system somewhere. In older tanks, there's going to be a great deal of it in the rocks from a few different sources. Cyanobacteria doesn't care care whether the phosphate is in the water column or the rocks, if it's there and accessible, and it has everything else it needs, it will grow.

The idea that reducing the total amount of dissolved phosphate in the tank could somehow make phosphate more available to cyanobacteria doesn't make sense. In a tank with no cyano problem, one of three possible states is true:

1. There is no cyano in the tank (virtually impossible if you've ever added a coral, fish, or piece of live rock from another tank or the ocean)
2. There is a cyano predator keeping it in check (if you could identify this predator and breed them, you'd be rich. Or rich-ish)
3. The nutrients needed for cyano to become dominant are not available in sufficient quantity.

Case three is most likely. If you add one chemical intended to lower the level of one nutrient (GFO, biopellets, etc.), and then you see an outbreak of something like cyano, it is far more likely that what's actually happened it that you've not reduced the target nutrient low enough to become limiting to said organism, while adding another nutrient that previously was.

I'm not saying you need GFO for cyano bacteria to grow. What you need is all the nutrients it requires to become dominant present in excess to grow. Old rock in new water might be a perfect example of that case. We only do 10-20% water changes at a time, so without intentional addition, over time the iron levels in a tank will fall, especially if you've got algae of any kind growing. 100% new water has whatever background iron levels were present in the salt mix (potentially quite high depending on the source), and nutrient laden rock that, depending on the rock, has the capacity to raise dissolved phosphate levels by 0.5 to 1 ppm in a couple of days.

I agree there is cyanobacteria in the water column to some degree, but the kind of cyanobacteria that forms mat-like biofilms that are problematic in reef tanks are most likely not the kind that have much or any of a pelagic phase. The mat forming cyanobacteria that we deal with are probably species from the genus Oscillatoria, which form long, oscillating filaments that form dense mats on top of substrates. They reproduce by fragmentation, and unlike dinoflagellates that can let go of the substrate and move in to the water column and swim around, the only amount of time most Oscillatoria species spend in a pelagic 'phase' is when hormongia (lengths of filamentous segments) break off from a parent colony and get blown to somewhere else that they settle to start a new colony.

Pelagic cyanobacteria are from a different group of genera and are mostly non-colonial forming, single celled organisms that wouldn't last long with a protein skimmer and even the smallest amount of mechanical filtration. The exception are species from the genus Nostoc, which can form massive floating mats (perhaps what you've observed in tanks with poor flow), but under adequate flow and decent filtration they'd likely be quickly destroyed and removed. Basically I'm saying that the kind of slimy, substrate coating, mat forming cyanobacteria that we deal with don't pick between being in the water column or being on the rocks depending on conditions. If you're seeing more cyano on your rocks tomorrow than you saw yesterday, it's because the total mass of it in your tank is increasing, not that it's picking a substrate bound state over a pelagic state (otherwise our tanks would look like a red tide).

I picked up Phozdown tonight, but stupid home depot sent me on a city wide run around looking for the half inch PVC fittings I'll need to modify my manifold, so I won't be able to set it up until the weekend.

I also picked up a 100 micron filter sock, and some 50 micron filter fabric to put in it that will live in the filter second filter sock holder in my sump that I've never used to dose the phozdown in to. I'm a little nervous about calibrating it all properly as I don't really trust most phosphate test kits (thus it's hard to trust the "rate" at which phosphate is added to the tank), but I'll start slow and see how I go.

I don't know what section of town you're in, but I find that Rona at Crowfoot has the best pvc fitting selection.
I started out dosing 1/2 the recommended daily amount of Foz Down.
For measuring phosphate I use both the readout from my Hanna tester and the appearance of existing macro algae to tell me if things are going in the right direction.

Which Rona? When I left the 16th Ave Home Depot I called the Bowness Rona because they're the closest but they said they didn't have anything smaller than 2" fittings. The guy at Home depot said they were the only ones that didn't carry the small fittings though, so I drove all the way to freaking royal oak (after their plumbing department wouldn't answer their phone) and they had the exact same selection as 16th ave. I hadn't eaten dinner yet, so I was hangrily fuming. The next closest Home Depot would have been Country Hills, but that's practically driving to Airdrie and they wouldn't answer their phone either.

Rage.

What 1/2 inch fittings are you after?

For plumbing fittings I have flat out stopped going to Home Depot, very little selection and horribly organized. Hit the Rona's. Guy on the phone I'd an idiot. Have 2-3 time the selection of Home Depot and way more organized. I use the one on McLeod and southland but the crowfoot one is good as well. I live south so it's easier.

Before you start your LC dosing (which I have not done, so only passing on what I read), I know that Reefsupplycanada used to sell 10 micron socks to use with Fozdown. I would hate to see your tank suffer another mysterious set back that may be ultimately traced to LC flocs that escape your 50 micron net.

Crowfoot shopping area is at Crowchild Trail and Nose Hill Drive nw.

That's a good idea. I wanted a smaller micron sock than what I could get at wai's. And as for set backs... If the tank looked the way it did a year ago, I'd be way more cautious about this. But when you've not got much else to lose, it's less scary to experiment.

90 degree elbows. Got to get a pipe from my rerun line back to my filter sock area

Dangnabit. I basically drove right past there on my way to Home Depot.

So, you're advocating using roughly 50mls of GFO in my 105 system, instead of the BRS recommended 225mls ? ( For my tank they recommend 0.86 cups )

Your ammount equates to;
105/30=3.5 Tbsp
3.5x15mls(Tbsp)=52.5mls

I get all the hype about selling product and such, and some may not change their media when they should, but that's a big difference

I'm asking as I'm considering your recommendation for 3 reasons;
1 - I have GHA that I suspect is living off the iron from the GFO
2 - My corals have become 'too green' after the last GFO I bought
3 - I'm looking to cut costs

I'm also considering cutting GFO out of my tank's diet altogether as it's getting old enough now

Gfo is like any other product, the amount you "need" to keep phosphate levels at a certain set point won't ever be determined by tank volume.
It will be determined by the rate of addition of phosphate. You could have 10000 gallon tank with three fish and brand new ceramic rock, and you'll probably need less gfo to keep phosphate at "reef" levels than a 300 gallon tank with 40 fish and 7 year old rock. Whether "less" means smaller volumes changed more often, or huge quantities changed every 3 months, the amount you need is dependent on the amount you use. Just like carbonate or calcium.

Gfo can certainly reduce phosphate levels. My... Question (I guess?) is whether gfo can reduce phosphate levels to the point where the extra iron, in some cases, doesn't negate that benefit.

Foz Down alone can remove phosphates to the point(150ppbillion) where it is not reliably tested by most electronic meters, meaning the meter's margin of error is greater than the phosphate level. With Foz Down there is no need to use GFO and suffer with the other issues that GFO and reactors bring along.

Wai's should have 10 micron 4" diameter filter socks.

He didn't seem to, but none of the socks I saw there listed the micron size. He didn't think any were smaller than 100 micron.

They are the 10 micron socks at Wai's.
They're the same ones I got from Tim.

I got the smaller micron socks. Had to put it inside a larger square sock as my square holders are just the tiniest too big for them.

Next step that's frustrating me is this freaking Hanna LR phosphate test kit. It's been months since I bothered testing for phosphate because of this issue. Test 1: 33 ppb P (about 0.1 ppm po4). After a water change a 1ml dose of phozdown (probably to small to do much in my size tank), test again. 44ppb P.

Do a dummy test with pure distiller water... 22ppb.

Glass vials are notorious for adsorbing small amounts of phosphate. In high end labs, they wash the glassware they use to run phosphate tests in hydrochloric acid regularly to remove it. The last time I was regular testing P, my "level" was predicted by how many tests I'd done, not what was actually in the tank.

Anyway I just acid washed and and dummy tested my vials again and I'm down to 16ppb with distiller water, which might be the actual amount in the water jug I bought from Safeway, but it still makes it hard to trust the test.

Yes. I've had better results in the tank by using a lesser amount and changing more often.

I just looked at BRS, as I'm not familiar with their recommendations, and I see they want you to change it out every 4-8 weeks.

To compare my recommendation to BRS:

My recommendation is 1 tbsp (15 mL) per 30 gallons changed every 2-3 weeks. So my recommendation on 105 gallons works out to 140-210 mL in 8 weeks. I use RowaPhos strictly. I haven't used BRS HC GFO in several years.

BRS recommendation of 225 mL of the HC GFO changed every 4-8 weeks is 225 mL to 450 mL in 8 weeks.

There is almost no data available to compare the different brands of GFO, although I have found one comparing RowaPhos to PhosBan. http://www.theaquariumsolution.com/f...n%20report.pdf

Ultimately, my recommendation is based on using RowaPhos, and I am not sure if my recommendation can be directly compared.

In response to post #14 by Asylumdown. http://www.canreef.com/vbulletin/sho...8&postcount=14

Some points to understand...

Test kits only read inorganic phosphate (PO4), and cyano can use both organic and inorganic phosphate. GFO only binds inorganic phosphate (PO4).

The red (or green or brown) stringy gunk we see in the system is not the cyanobacterium. That "gunk" is what the cyanobacterium exudes, and the bacterium is under that, and to a degree within it as well which is a method of spreading (aka hormongia aka motile reproductive filaments).

Cyanobacteria are biologically really cool - they don't follow the usual rules. Cyanobacteria are autotrophs, and the species that we see are also able to fix atmospheric nitrogen (which is really cool because cyanobacteria are aerobic and nitrogen fixation requires anaerobic conditions). Cyanobacteria are particularly good at surviving in both iron-limited and phosphate-limited environments.

Indeed the cyanobacteria we see in our tanks is benthic (clings to the surfaces). When I say the bacteria are in the water column, this is not something you can see. The hormongia are much different than pelagic cyanobacteria.


I think you're over-thinking my use of the word "balanced". The balance I'm referring to is simply that the water column contains roughly the same amount of phosphate as the substrate (sand/rock).



I think we are "arguing" different points. It appears to me that your side is that you think cyanobacteria are triggered by iron, where I believe cyanobacteria are triggered by phosphate imbalance within the system.

My own experiences (and yours also, it appears) have shown that adding a large amount of GFO to a tank can ultimately cause abundant growth of cyanobacteria. Seeing as cyanobacteria are not responsive to iron-limited nor phosphate-limited environments, then it must be something else.

At least in the case of the cyano we deal with, no, that's not the case. I can post some pics of what the red slime from my tank looks like under my microscope when I'm back at a real computer, but that red "slime" is made up of hundreds of billions of strands of long cyanobacterial filaments (most likely from genus Oscillatoria). The slime is the cyano. Within that matrix there are also several species of diatom, a couple microscopic worms, lots of heterotrophic and chemo-autotrophic bacteria, and dinoflagellates, but the aggregate thing that you see - the red slime - gets its colour and texture from the cyanobacterial filaments that make up the scaffold that all those other micro critters live within.

That red slime isn't just cyano, it's an entire self contained microscopic ecosystem.

They are cool, I will agree with that. The exact nitrogen fixing capacity of the kinds of cyano we deal with (as I said, likely Oscillatoria) is still being debated, as they lack heterocysts (the structure all other cyano species use to do it), but they seem to have evolved their own structures for accomplishing the same goal. And yes, it's a highly oxygen sensitive process, too much O2 and the enzyme responsible (I think nitrogenase) breaks down. But yes to all of what you said, it's why I think iron from gfo drives its presence in a tank. If you're good at scavenging something from an environment that is usually available in limited supply, you've got all the ingredients you need to become totally dominant when those nutrients are provided in excess.

Cyano is also likely uniquely adapted to using the kind of iron found in GFO compared to all the other organisms in your tank. They emit organic molecules called siderophores that specifically react with inorganic, oxidized forms of iron and turn it in to something they can easily absorb. This makes then capable of living in iron limited environments. It makes them excellent at living in iron rich environments.



Right, the point I was trying to make is that there's no significant growth of cyanobacteria in the water column. Any cyano that is in the water column is a fleeting transitory stage as hormongia get blown from point a to point b. The amount of hormongia in the water will be entirely dependent on the amount you have growing on the rocks (just like the amount of dust in the air is directly related to the amount of dust being stirred up from the ground). You'll never have a scenario where there's lots in the water but little to none on the rocks because of some phosphate "balance". Not in an established tank with an effective protein skimmer anyway. If there was significant cyanobacterial growth happening in the water column, it would be a different genus from the slime you see on the rocks altogether, and you'd see it. Your tank water would be cloudy and tinted red or green.


I'm saying it doesn't matter if they have the same concentration or not (and they never will, fwiw). If the water has a high concentration, it has access to easily available P. If the water has a low concentration and it's getting it from the rocks, it still has easy access to excess P. Cyano doesn't care about the balance, it cares about whether the nutrients it needs are available or not. Reducing the concentration of phosphate in the water column does not somehow make phosphate more available.

If you have high phosphate in the water and no cyano growing either:
1. You don't have cyano present
2. Something is effectively predating the cyano
Or 3. Some other nutrient or environmental condition is limiting its growth.


My argument is that I don't think the idea of a phosphate "balance", in this scenario, is not a real thing. Nutrient balances in nature and how they influence a competitive regime are a thing, but unless you've got a massive refugium growing tons and tons of macro, there's not really anything in a tank to compete with an organism as fast growing and aggressive as cyano. Low P in the water, high p in the rocks, or high P in the water, high P in the rocks - cyanobacteria doesn't care. If it's in a form or location that it can access, it will use it. Being triggered by rapidly lowering P in the water would require cyanobacteria to have been politely ignoring the cheapest, easiest to get at, most readily available form phosphorous we know of.

Given how little P it needs relative to N and C, and how good it is at scavenging it from low P environments, and that (as you mentioned) cyanobacteria can use forms of phosphate not readily scrubbed by GFO, it's far more likely that no reactor you could buy has the adsorbing capacity to reduce phosphorous levels in your tank to the point where it would be limiting to Cyanobacteria. All your corals would die if you did. In the rocks or otherwise.

What you are supplying, however, is large quantities of an atom that is differentially vital to Cyanobacteria for survival; that isn't regularly dosed by most people; is found only in trace amounts in foods and most salt mixes; and is in a form that organisms other than cyanobacteria will probably have a hard time using.


It's not that they're not responsive to low iron/low phosphate environments. It's that they're adapted to surviving in them. Take an organism adapted to surviving in an environment where some critical nutrient is limited and provide that nutrient in excess, you get steroid-like growth.

I'm curious how you have come to the conclusion that the cyano in our tank is likely Oscillatoria? Is that your own ID from your microscope or are you reading this in your research?

I see your point, and I understand your observations. I don't think your theory of steroid growth is always true though. I could think of a million examples, but the simplest one I can think of off the top of my head is sunlight for photosynthesis. Too much light can actually cause photoinhibition. So too much of a good thing isn't always better.

I think the ideas are interesting, but I also think there is more to it. I don't think it is as simple as adding iron via GFO. There are too many instances in my mind where cyanobacteria have popped up and it would be tough to blame it on iron. It makes me think about what the cause may be in those instances. Since cyanobacteria are such amazing critters I imagine there are many situations that could cause the growth. I'm also sure I've seen at least a dozen different species of cyanobacteria in saltwater systems.

I like this discussion though. It is discussions like these that get us thinking in new ways and solve old problems with new ideas. :)

Yes, I'm definitely over simplifying it, as cyano has been a problem for as long as people have been keeping salt water tanks. In nature there's probably lots of cases where the nutrients needed for it to grow are present but it still doesn't, so there's a lot of complicated interactions going on. One paper I read even hypothesized background levels of hydrogen peroxide, which can naturally reach as high as 0.36 ppm in some parts of the ocean, might inhibit huge amounts of cyano bacterial growth (reactive oxygen is particularly deadly to cyano's photosynthetic structures).

You also have predators that we probably don't keep in tanks, bioturbation on a much larger scale, stronger wave action, and more things to compete with it.

I'm sure we could also find lots of tanks that deal with cyano that don't use gfo.

But, when you've got it, or are fighting it, I think it's worth considering that what has been long touted as a cure might in fact be part of the problem if gfo and low tested phosphate isn't slowing it down at all. There's good, supported science to suggest a link, and a long evolutionary history that makes cyano uniquely adapted to turning your best tools against you. In researching some background for this thread I even found an article where they assessed how good glucose and fructose were at making different species of oscillatoria grow (sad news, sugar dosers).

Fwiw, I'm on day three of phozdown dosing and I'm either wishfully seeing things, or my cyano population is down by 25%

oops, missed that. What I get for typing on an iPhone all day. I was curious about it because there's so many species out there so I started looking in to cyano taxonomy. The Smithsonian Tropical Research Center maintains a great site with pictures of different cyano species in the wild, and Berkley also maintains a pretty good (if unsophisticated) site on cyanobacteria as well. The different genera are pretty distinctive in their behaviour, morphology, and appearance. Oscillatoria is the only genus that fits the bill as a group. It's the only one that forms mats of slimy 'cyano' like substrate coating goos in tropical marine environments. You can look at a bunch of pictures here: http://biogeodb.stri.si.edu/pacifica...lue/flocculent

Going beyond genus to species would take a microscope way better than mine, and even people who are experts on this as a career never seem to agree. This is what it looks like under my super crappy microscope (it's a video so you need to click on it):

http://i1100.photobucket.com/albums/...ps67cc7b9d.mp4

That magnification wasn't high enough to see the heterotrophic and chemoautotrophic bacteria that live in association with the cyano mat, but you can see the super cool stretched out diamond shaped diatoms and a couple of the watermelon seed shaped dinoflagellates that live in association with the film. It's called "Oscillatoria" because the filaments re-orient themselves by oscillating back and forth until they are positioned as best as possible to receive the light, which is why the strands look like they're vibrating. I think it might be part of why cyano mats seem to shrink at night, the entire colony can deflate at night, then puff up over the course of the day as individual filaments stretch out to try and get the most light.

FWIW, based on those pictures, O. margaritifera, O. okenii, and O. subsalsa are great matches for the kinds we typically do battle with.

Well just thought I would put my 2 cents in. I had Cyno start to appear and this is what worked for me. Pull the GFO and GAC get some Seachem Purigen like 1L and pick up a few of the Seachem " The Bag" works perfect for the Media as it is fine. You can put it in the sump or better would be a small Canister or if you have an AquaClear hang it on the back or side. I did this and within the first day you could see the Cyno start to disappear and your water will sparkle. This stuff lasts quite a while and can be regenerated. It rapidly removes Organics from the water.
One other thing maybe I missed it but is your skimmer working as it should?
The other thing maybe lights old tubes or bulbs if you are use them.
Give the Purigen a try, its simple safe.
The other thing I just thought of that seem to help also was Brightwell Aquatics-Microbacter 7, with a large tank you may need to get the 2L bottle.

Good luck.
All the best.

Mike
P.S one other thing you can try if you use the Purigen is cut back the lighting time or shut them off for 2 to 3 days. That should get ride of the stuff real fast.

Thanks Mindy ( I missed your post ) :wink:

I've been using 225ml and changing it every 2 weeks
I'll try cutting it in half to start with and see what happens with my PO4 readings/algae issues

If all is good I'll keep cutting it back to a point where I know what amount to use every 2 weeks