chris_h--the reason that you shouldn't just keep using CaCl2 is that you're not adding any alkalinity component to your system. Alkalinity is responsible for your system's ability to avoid large swings in pH. If your alkalinity plummets, pretty soon you've got a situation where you can't keep your pH supported. A little extra food or a dead critter, and BAM, your pH drops like a lead balloon, taking your livestock with it.
Also, as mentioned above, in order for corals and other calcifying life to grow, it needs both Calcium ions AND carbonate ions in solution. Without both simultaneously, no calcification can take place.
Hopefully, your water params will be OK. On the long-term, however, it's possible your Ca level will get so high that your alk will plummet, you'll end up with no appreciable growth in any calcifying life forms, and you could also experience a pH crash that could devastate your system. Incidentally, the general consensus is that CaCl2 is not really designed for long-term use, but only for balancing your water chemistry. Once your system is balanced, you should be using balanced supplements like kalk or B-Ionic, or a Ca rxr.
I generally don't recommend CaCl2 and sodium carbonate/bicarbonate on a long-term basis as a supplementation system. Rather, each of these can be used independently if there is an imbalance of your system's biomineral components, but once the desired balance is achieved, a balanced approach is preferred. For an explanation of why CaCl2 and sodium bicarb are not good for long-term supplementation (causing increased SG and ionic imbalances), see this
article by Craig Bingman.
Get some test kits. Mess with them until you learn how to read them. Then you might consider supplementing Ca and alk using a balanced approach once you find out where your numbers are.
