Yes and no, they all do the same thing, maintain Ca and alkalinity levels. Ca reactors have a high initial cost, and can be tricky to use, but in some cases its worth the $ and the effort, they are best on tanks containing a large population of fast growing sps corals and clams. kinda over kill for the average tank unless you have the $ to blow. Kalk is cheap, especially if you use pickling lime from a grocery store, although it is caustic and can have a serious impact on the overall pH if not used carefully. 2 parters can be expensive, and in most cases they have to be added every day at a certain time, but they are simple to use. IMO the best thing to use for the average reef tank is kalk, its easy to set up a drip system, and you can kill two fish with one stone, maintain Ca and alk levels, and replenish water lost through evaporation. Just be carefull not to add too much to fast. HTH
