Karin, yeah Cory pretty much described the problem with using calcium chloride. Eventually you get to a point where it's almost impossible to maintain alk/calcium/mag level because everything keeps precipitating out of the water. Two part systems are supposed to be ionically balanced so you don't get into that situation. Although I think if you went long enough without any/insufficient water changes you could see it happen even with the two part since they're never going to be perfectly balanced. So if you ever get to where you're having to add more and more and more of your two part just to maintain levels and your not getting lots of growth to account for the increase then it's time for some big water changes to set things right again.