All of the above are good points.
Although it might look like easy to keep they require as much care as SPS corals.
An animal would not move for no reason, something had changed; think about what did you change in the tank. Did you move rocks, changed flow or lighting intensity?
May be water change is due? Chemical warfare is definitely a possibility and you should use chemical filtration regardless if you have mixed species tank.
Your main goals would be:
1-Clean water (chemical filtration
http://www.jlaquatics.com/phpstore/s...t_ID=bd-cpre10 , activated carbon, phosphate removal, skimming and regular water changes)
2-Flow (some species like more some are looking for quiet place, do your research
3- Feeding; if anemone does not take food do Not force it its mouth, just do you water changes regularly. If it does not eat try small particulate food like ReefRoids
http://www.jlaquatics.com/phpstore/s...t_ID=plb-rr004, or this
http://www.jlaquatics.com/phpstore/s...uct_ID=DT-OE15 , so anemone can get some food with the flow.
JMTCW