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.