Sorry for your loss. If you decide to try another anemone later, I think your issue was your lighting. My main tank has T5 lighting and I recently set up a second tank to play with LED lighting. I moved a one-year old rainbow BTA to the tank with LEDs and within a few days, it did exactly what your nem did, released its zooxanthellae, not waste. I moved it back to the main tank under T5's and he recovered quickly.
I underestimated the power of my LEDs and fried several SPS corals as well. I raised the lights 4 more inches and lowered the intensity, and SPS are doing fine now.
When water parameters are within range, lighting is generally the culprit in my experience.