I have used GAC at times for 30 years. No HLLE. Coconut shell, bitumulous and pellet mostly. Wash it well, don't let it tumble and avoid Lignite if you feel bad about it. Lignite could just as easily release something that is a problematic just as much as it was dust/fine - both could get filtered. Was the dust/fine ever found in areas of the fish that were an issue during autopsy?
Does anybody know what is in ROX? A cocktail, I would guess?
Yes - after I published my study, I was contacted by a researcher in California who had incidentally found carbon fines in the lateral line pores of some fish using SEM. Trouble is, he didn't write it up as that wasn't part of his study at the time.
I should add that the team at Disney feels that it isn't the dust per-se, but that carbon removes organics, which are normally bonded to heavy metals, rendering them less toxic. They feel that removing those organics allows for higher free heavy metal levels and THAT causes the HLLE. Two issues with that hypothesis: 1) in our study, we used newly mixed seawater that had no heavy metal issues and 2) if marine fish are challenged with heavy metals (copper or zinc anyway), they don't develop HLLE (grin).
People using carbon and not seeing HLLE is pretty common in the reef community. As my write-up says, there are exports of POC (including carbon fines) in reef tanks such as protein skimmers and the filter feeding invertebrates that tend to reduce the issue. We did find that even pelleted carbon caused HLLE lesions, but they were smaller and only showed up during histopathology.
Jay