My tank has been running since dec of last year, and yes only alk, the only time i add calcium is if for some reason i add a little more alk than needed just put a little calcium in to bring back the balance. maybe you could spend that money on a frag or something else but if you are looking for a dual reactor and that is the way you want to go let me know i have one laying around somewhere that i haven't used since my sps tank crashed a few years back.