I see newbies buy fish that they would be better off leaving at the lfs or in a more experienced keeper tank. I thought that it would be nice if some of us that have killed more stuff 
over the years gave them a little pre-warning.
Please feel free to add to this I'm only going to discuss a couple of fish and groups that I see people kill quite a bit.
Tangs
Tangs are not easy they are sensative to water quality, space issues , and are ich magnets! Most species need at least a 75 gallon tank with lots of swimming room. They have been know to take out whole tanks with their introduction of ich. These fish must be put in hospital for at least 6 weeks prior to introduction.
Mandrins-
They need at least 50 gallon tank with 1.5 to 2 lbs of l.r. per gallon. All they will usually eat are pods so DON'T buy one with the hope of getting it to eat other stuff," you have about a 20% chance IME." They also do very poorly in tanks with anemones.
Triggers and Puffers
Lots of these guys get big and mean . Do your due dillagance prior to purchase of any of these beauties that tiny little boston bean is going to grow into a 2ft monster. They are wonderful but, know what your buying and what it's going to do to what ever else you have.
B-flys
Again know what you are getting. Some of these are MUCH easier than others. You also want to avoid adding fish like tangs they won't get on very will with a b-fly at all. They also need to be in a F.O. set up or they will eat your coral.
here are a few everyone else chime in. Only one request lets keep this geared to newbies,"6 months or less experience" and we don't wan't to overload anyone. If they have questions they can post.
Chris
over the years gave them a little pre-warning. Please feel free to add to this I'm only going to discuss a couple of fish and groups that I see people kill quite a bit.
Tangs
Tangs are not easy they are sensative to water quality, space issues , and are ich magnets! Most species need at least a 75 gallon tank with lots of swimming room. They have been know to take out whole tanks with their introduction of ich. These fish must be put in hospital for at least 6 weeks prior to introduction.
Mandrins-
They need at least 50 gallon tank with 1.5 to 2 lbs of l.r. per gallon. All they will usually eat are pods so DON'T buy one with the hope of getting it to eat other stuff," you have about a 20% chance IME." They also do very poorly in tanks with anemones.
Triggers and Puffers
Lots of these guys get big and mean . Do your due dillagance prior to purchase of any of these beauties that tiny little boston bean is going to grow into a 2ft monster. They are wonderful but, know what your buying and what it's going to do to what ever else you have.
B-flys
Again know what you are getting. Some of these are MUCH easier than others. You also want to avoid adding fish like tangs they won't get on very will with a b-fly at all. They also need to be in a F.O. set up or they will eat your coral.
here are a few everyone else chime in. Only one request lets keep this geared to newbies,"6 months or less experience" and we don't wan't to overload anyone. If they have questions they can post.
Chris
OG