As far as your daughter trusting the LFS
guy, I would say as long as he/she was giving good advice for the tank, she should continue asking him questions and for advice. But so far it sounds like his advice might be a little off. Now, that doesn't necessarily mean that he is giving her the wrong info just so she will buy more product from him, although I have seen that be the case in alot of situations. He/she just might not know the right info, or they think the info they know is the right stuff. I used to trust my LFS
until I found out that I got burned with bogus sales and info. Now I don't ask them any questions at all, I get all my advice from this forum and have never once been given bad info. The people on this site are very friendly and EXTREMELY knowledgeable. As was suggested by Kevin earlier, I would invite her to browse this site and see what she thinks!