As far as the tang and the tank size, I won't beat a dead horse, but that probably is some of the problem. The other being, it's trapped in there with a territorial Damsel.
Like other post stated, most LFS
will say anything they can to make a buck...anything.
It's up to the end user to know what's best for their situation. They do make reference apps for iPhone and I'm sure droid, that have basic stats for fish and corals. These can be valuable while at the LFS
. Then you aren't relying on them for info., and susceptible to their mis-information.
Honestly, if you want what's best for that tang, put it in your tank at home ( it's twice the size of the 10g.). And start thinking about at least a 125g.
Best of luck moving forward.