Hello....
Actually, calcium chloride is used as one of the primary ingredients in the two-part calcium/alk supplement. The other ingredient is sodium bicarbonate.
Yes, adding primarily calcium chloride to your reef tank is a bad thing since you will have excess chloride ions. However, if you add the right amount (aka ionically balanced amount) of sodium bicarbonate (baking soda) or sodium carbonate (pure unscented washing soda), then you will no only add bicarbonate and carbonate (which is another word for adding alk), but you will be adding sodium to the water. Sodium + chloride = salt. Okay...so now your salinity is going to be affected...a bit. But...this is a small side effect of most 2 - part solutions. So...if you want to add CaCl in the long term, you might want to add an ionically balanced buffer with it too
I admit that 2 part solution calcium additions are not perfect, but calcium reactors and kalk mixes aren't perfect either. Each has their advantages and disadvantages.
- Victor.