Mandarins deserve a considerable amount of respect.
If we are choosing to keep them, we must be prepared for them and do all that is in our power to provide the foods they need. Unless you have a large tank with a considerable amount of Live Rock, you will need a pod culture setting up. You need to be prepared to purchase pods to replace your culture if your culture crashes. You must also be prepared to work hard to train the Mandarin / s to eat other food to supplement their diet.
It is wise to choose a Mandarin that has fed on frozen food in the shop, you should look for a plump mandarin, the breast bone should not be showing, from underneath the mandarin should have a plump belly and not be concaved and when you look from the top you should see a very gradual decrease in body thickness from the front to the tail.
The mandarin should be aler and constantly moving, a still mandarin is not a healthy mandarin, they search for pods constantly as such should always be on the move.
I have included a link to my Mandarin Love thread where I shar my experiences and show how to set up a culture.
Don't hesitate to ask any questions on the subject, it is far far better to be very well prepared with these fish and to remember they need a mature tank.
It is also wise to choose the largest mandarin you can find, smaller ones IMO / E do not do as well as the larger fish.
Mandarin Love Thread