Lemon peels are a definite no no for reef tanks. I think you made the right choice in taking the tang back, remember the LFS is a business, their goal is to make money. Unfortunately, some will sell you inappropriate things to make a $$.
:shock: Biffer, how can you say such a thing about a LFS. It is my job to be the cynical, judgmental and critical person. Your the nice patient type, that usually says nice things. :D