So I never replaced the carbon or the GFO. I don't know that it was chemical warfare. I think my alpha male clownfish was eating it in response to a clutch of eggs and competition from 2 other male clowns in the tank. A day or two after the nem was trimmed down to nothing the clown died mysteriously. He was a several years old and had been bonded and breeding with the female for few years. I was not able to examine the body since he was being eaten by my coral banded shrimp in the center of the rock pile. Now a couple of weeks later the nem is recovering and the tentacles are growing back.