Iron, GFO, and Cyanbacteria

[asylumdown]

The amount of extractable ferric ion from GFO should be very, very small. It would not be unreasonable to assume that cyanobacteria can reduce this to the more useful ferrous ion. Is GFO the cause of persistent cyanobacteria growth?

If the hypothesis is that GFO does encourage cyanobacteria in aquariums, no one has done an appropriately comtrolled experiment to support the notion.

You are correct, but there's been plenty of studies on the link between iron and cyano in the wild. Suspecting a connection in an aquarium isn't a tenuous jump.

Cyanobacteria will be found growing/not growing in the presence of a high level of phosphate or with an undetectable level of phosphate. Ditto nitrate. Ditto iron. Ditto in the presence or absence of GFO, GAC, skimming, filter socks, water changes, flow, light qualty, etc. No one factor can by itself has ever explained the presence or absence of cyanobacteria growth in aquarium.

Also correct. I'm just one data point and all I have is correlation to go on. There are other possible explanations for what I've seen - it could simply be a function of time: my tank aged enough for cyano to start appearing coincidentally around the time I switched from a polymer coated brand of GFO to "traditional" GFO type products. That could also be the case now, my tank was cyano free for the whole time I was using lanthanum, but I had dosed chemiclean to clear out the cyano not too long before I started lanthanum. Appearing right after I switched back to GFO could have just been a coincidence.

The only place I'd say you aren't totally correct in your above statement is that cyano will grow in either detectable or undetectable levels of the nutrients. While technically true in this context, there is a serious mismatch between scientific studies on limiting levels of nutrients in groups of organisms (and I'm not sure there's much published to this regard for all the elements we're talking about in cyano's case specifically) and our ability to resolve those same nutrients within our aquariums. Our ability to test iron and total available phosphate, at the hobbyist level, is pretty terrible, so 'undetectable' in the context we use it doesn't really mean much to an organism like cyanobacteria.

No one ever leaves cyanobacteria bloom alone, so, we don't know what percent of outbreaks resolve by themselves. When remedies are tried, rarely is only one remedy tried at one time and never is only one change at a time made in the aquarium. We basically don't know why a particular case of cyanobacteria is resolved or in your case not resolved.

The exception to these observations about remedies is Chemiclean. Chemiclean does seem to be a fairly reliable remedy, though not without risk and not foolproof. Lights out might also be useful but it is probably not as reliable a Chemiclean.

It sounds like the cyanobacteria has become a resident in your biological filter or microbiome and that no other organism is going to drive it out. You might try dosing with bacteria to disrupt its current hold. This probiotic remedy though is a new idea and unproven.

You might as well bite the bullet and use Chemiclean. A year is a long time to deal with cyanobacteria.

I've used chemiclean multiple times. It does a great job, but it always comes back. I doubt it would ever be possible to kill every single filament of hormongia in an entire tank without pouring a large bottle of bleach in the water and walking away. I've found hydrogen peroxide to be extremely effective as a spot treatment. I turn off all the pumps and use a 1mL syringe with a super fine tip to administer it right to cyano patches. There's research suggesting hydrogen peroxide is selectively toxic to cyanobacteria at relatively low concentrations, so it theoretically has some systemic benefit, but applied directly it kills it in a matter of seconds.