Okay here is my mandarin history:
Had my green spotted mandarin in my 28 gallon for about two years (maybe more) before she got stung by my over-sized anemone and died
(I'm assuming it was the anemone since she was eating and happy the night before and she was a very fat mandarin so def not starvation)
Had a blue mandarin in our main tank for over three years, he was also eating prepared foods and was very fat. We added an evil niger trigger fish and that was the end of him and many other fish unfortunately.
We now have a blue mandarin in our large display tank who we added just over a month ago. she was eating prepared foods at the store and is still just as fat.
Also I replaced my green target goby after she died in the nano for another one. She has been in there for at least 6 months and doing well.
must get the best mandarins, I have never had a problem getting them to eat prepared foods.