Someone once told me that even if you use the best salt but don't do water changes regularly, the big 3 will drop and then you will have to dose...
I guess if you have a huge tank, it's tough to do a weekly water change. I always thought the nice SPS tanks we drool about, their secret is dosing. I'd imagine if your tank is packed with SPS, they'll quickly suck up the CA/Alk right?