Ya, Ca(OH)2 is better and cheaper than CaCl2. However, you can't add so much of Ca(OH)2 due to the high pH, and esp. when you don't have a lot evaporation. Meanwhile, you can add a lot more CaCl2 powder if you want to boost your Ca level up quickly. Also, if you have a lot of sps and clams, you may still need to add CaCl2 once in a while to keep up w/ the large Ca consumptions from your sps/clams