Chocolate chip starfish are not reef safe. They can eat a variety of things including corals, clams, and other starfish. There are many reef safe starfish, yours just wasn't one of them unfortunately. If the anemone dying killed the fish, it was probably because the anemone death caused a spike in ammonia which the bacteria in your tank were not able to handle and that killed the fish. You're probably in the middle of another cycle with all that death. I'd measure your ammonia and nitrite to see where you are there. Also, a little off topic but because you said you're new...anemones are very sensitive and difficult creatures to keep alive. They require very good water quality, high light, and stable conditions. Its best to hold off on them until your tank is at least 6 months old, to give the tank time to mature. There's a lot of other factors beyond just the initial ammonia/nitrite cycle that over time make the tank mature, fully cycled, and more prepared for sensitive creatures. If they do die, especially in smaller/newer tanks like yours, they can take a lot of other life with them when they cause another cycle, like unfortunately happened to you.
Good luck restocking! Take your time, post plenty of questions, there are lots of people here willing to help.
