[asylumdown]

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).

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.

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.

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.

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.

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 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'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.

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 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.

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.

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.