You guys are a hoot! I usually run activated carbon, RINSED very well. I'm too lazy to read the article so thanks for the cliff notes! I believe (not a scientist so I don't have to prove it to believe it) that it is more nutrition based than anything. You have to remember that running carbon can strip nutrients from the water that may be needed by the fish, and the lack of these nutrients could be the cause as well. I would have liked to see what happened to the 3rd tank after the study if carbon was introduced to that tank. And for the record, this HAS been around for years, and years, and years - this is not new. Erik, I haven't heard of immediate HLLE as a result of adding carbon, so your results surprise me.

I'm so glad Allan has clean water now so we could have this chat!