I figured you had considered this. It is just such a mystery. I lost a few shrimp and fish mysteriously as well. One fish I lost did have an intestinal issue that quickly killed it. Because of the loss of fish and invertebrates, and the fact I had Pacific live rock, I watched for a predator. Never found one though. I also considered toxins as I had a Toadstool Leather die and Palythoas being stung by the anemone. Never figured it out for certain and have had no further losses. Tank mysteries suck.