Welcome to the fine art of balancing calcium and alk
Go easy on the LFS. Having worked at one I can tell you its very hard to diagnose everyones tanks. We could only tell you whats recommended. Even after spending a half hour or an hour with someone i would still forget to tell them something, thats if we are slow, when its busy in there forget it..... There are so many variables to this trade no two tanks are the same and every tank can reach the same goal through very very different means....
EDIT: EVEN THEN i can tell something to someone and they will sometimes ignore it, like this lady who wanted and bought a Med Naso Tang, but didn't tell me she was going to the other LFS to pick up a Full Size Angel. Next day "my fish have ich" what can i do? Oh this was 55 or 75(can't remember).... Or the guy who wanted a 150 dollar french angel to put into a freshwater tank..... But he didn't tell us that and came back the next day wondering why it was dead....
There was always a certain assumption I took when people talked with me. I could usually tell who knew what they were doing or who had no clue....