theres alot in the hobby we dont understand ,you could try the same colony again and come out with a total different outcome this time and the thing about zoanthids as mentioned is they need different things some die fast some die slow, some want light some want little,some like random flow some prefer little flow.when your talking about a species of coral that has such vast requirements could be hit or miss on getting them to grow. its part of the fun of the hobby is trying to get things to flourish and if it was easy everyone would be sucessfull at it but its not and alot of things come into play and even more that we dont understand,this is why i mentioned that they are always misclassified as being a hardy or easy coral to raise.in your case it could be something as simple as too much light or something as complex as starved to death over time.unless it was something directly you did or noticed/changed chances are you wont get the answer your looking for just a bunch of what if's.keep trying different varietys and see what grows for you.cheers
