GFO and KH.

[daplatapus]

On another thread I was discussing my corals and their health. My LFS runs his frag tank at a KH of 10. My tank has, until now, been running around 8.0 and I was wanting to raise it up to 10 or so. In the conversation in that other thread, it was mentioned that I may have trouble since I was running a GFO in a reactor. I've been searching all over but haven't been able to see any relation between the 2. Is KH affected by running GFO and is there a point where the GFO filters out what I need to raise my KH?

[2thdeekay]

GFO does bind carbonates, it's one of the competing anions that interferes w/phosphate adsorption by GFO. Some GFO products bind more carbonate than others. pH is also a factor, increased pH decreases GFO binding of PO4 but increases binding of carbonate.

[daplatapus]

So if I understand that correctly, the more I try and raise my KH I'll basically plug up the GFO and it will no longer bind with any PO4 ultimately rendering my GFO useless. Correct?
Other than wasting GFO then, are there any potential detrimental effects to the water flowing through the reactor, no chemical reaction that would otherwise harm the inhabitants of my tank?

[Randy Holmes-Farley]

There are many factors at work here.

Yes, the iron released from GFO can increase some abiotic precipitation of calcium carbonate onto and just downstream from GFO being used. That can be mitigated a bit by not dosing supplements directly in front of the GFO intake, and keeping pH, alkalinity, calcium, and magnesium at reasonable levels.

GFO also, obviously, lowers phosphate, and lowered phosphate can increase the calcification by corals, and in turn, that appears as reduced alkalinity if dosing is unchanged. The answer: increase dosing as needed.

Finally, one other issues that some may refer to is that some SPS corals in some ULNS systems (such as zeovit) seem to have issues if the alk gets too high. Enough GFO may cause a similar issue, and so one might have “problems’ with higher alkalinity, even though the problem is not attaining the alkalinity level, but rather what happens once there.

All that said, I think GFO is a fine product, and I use it along with several other nutrient export methods (growing macroalgae, GAC, skimming, and organic carbon dosing with vinegar).

FWIW, I discuss GFO here:

Iron Oxide Hydroxide (GFO) Phosphate Binders
http://reefkeeping.com/issues/2004-11/rhf/index.htm