I am very confused after reading this link.
http://www.sciencedirect.com/science...18e88315e12b13

It appears they add iron into some charcoal as a benefit. If it isn't the carbon that is the problem I'll need to go back to the drawing board.

Anyway you can have the actual metal tested in the carbon? If you can verify its Iron then I would say its back to the drawing board but if its something else that could be your culprit. (That being said I do see what seems to be rust marks on the photos you provided which would lead me to think it is iron rusting...). Excess iron in the fish tank could attribute to some algae problems (Which would explain everyone with dinoflaggelets and slime) but should not be toxic at those levels (When I tore down my 54g I found 5 completely rusted razor blades in the sand :neutral:). Greg are you finding that everything in the tank is angry at you or just the coral? What ever the solution I hope you are able to find it fast!
Levi

So I found this at Physicsworld.com."It is also difficult to separate these small moments from the underlying "diamagnetism" of carbon. This is a very weak form of magnetism exhibited by almost all forms of carbon (and, indeed, by many other elements) in the presence of an external magnetic field. The external field alters the orbital motion of electrons and induces a small magnetic moment in a direction opposite to that of the field itself." AND the reason for what is most likely iron in carbon."The main cause for suspicion was that many of the reports claimed to have detected only small magnetic moments, which can simply be due to traces of natural magnetic contaminants. Iron, for example, is the fifth most common element in the Earth's crust, and its black oxide magnetite is everywhere in the air.

I am also experiencing issues. I have had RTN in long established colonies, and most of my smaller frags that I would peg as advance-expert, or expert types. I removed my carbon which look just as bad as Greg's photo, if not worse, and the RTNs have stopped. I did however loose an awful lot of colour from my tank. I also lost three clams, all medium sized; 4-6" inches.

I put my carbon in on the 26th, removed it late evening of the 28th, did a water change, ran new higher grade carbon, along with some other items, and as of today the RTN has definitely stopped. My remaining clams are out, and things are once again opening up.

I'm sorry this hasn't solved your issue Greg, but it definitely was the cause of mine. Thank you for posting this, it saved me even if there was some damage done.

michika were you using the HBH brand as well or a different type?

And does this problem involve the pellets or just the granular version of this particular carbon?

Things are definately improving with my system since I removed the carbon.

There are different pHs for various prepared carbons. I don't think it is the iron as iron salts are an additive in the Ultra products. I suggest it may be something else in the carbon another contaminant? Was there a large spike in algae growth, did any of your yellow sps start turning greenish/yellow? These are signs of overdosing of iron

A lot of hobbyists dose iron for their tanks to help growth of macro that they have in their tanks.
One japanese hobbyists uses a jar of nails in his sump from what I read on a post on RC.

ya I was kinda wondering that too because GFO is more or less just that, rust? Things that make you go hmmm....

Yes. I also have seen great improvement since I've removed it from my system. My tank is still recovering, my SPS hasn't yet returned to the same colours I had before.

If its not iron, it is something and it is linked to the carbon in my mind. It happened right after I put it online, and stopped after I took it out of my system. Either way I'm still thankful for this thread because I probably would have been struggling for weeks or months trying to figure out the cause.

Good to hear that your tank is rebounding Greg.

Chris

+1 And great that you figured it out for everyone, this had (potential) disaster written all over it.

This is not the first time I've heard of weird problems in a tank attributable to carbon. I remember about 6-7 years ago, AJ_77 had a reef tank that the water was continually green, huge huge phytoplankton bloom, nothing he did would cause it to stop getting greener, until he took off his carbon (which was some obscure, presumably cheap brand, which did say on the box "for FW only"). It went away a week after he switched brands.

Did some reading on carbons based on Greg's experiences, in one of the threads discussing it, there was a link to a discussion about carbon available from BRS labelled "ROX 0.8" .. long story short, it sounds really good. I went and ordered two packages for myself already..

ROX 0.8 is great Carbon, I have used it myself. We have access to this carbon as well as lignite which is also almost as good.

I have used the ROX and now only use the Lignite, its what i consider the best carbon available, its a bit pricey but well worth it as you can see in the above posts in this thread.
Cheeper is not always better.

I have a gallon of ROX as well, nice stuff but a lot finer than I expected. Its tough to keep it from clumping. I might try the lignite next time.