Still in "pain" over the loss of the Green Chromis I took a water sample to Exotic Aquatics, my local fish store (LFS). Everything tested perfectly. Ammonia - zip, nitrite - nil, nitrate - goose eggs, pH - a perfect 8.2, phosphate - not a trace. My water conditions were described as perfect. Must've been a fluke. Perhaps he was attacked in the middle of the night by some unknown creature that lurks in the shadows of my tank. So I decided to replace my Green Chromis. He is in his bag acclimating to his new home as I type. I hope this one decides to live longer than a day or two.