Personally I'd go with the Calcium reactor. They can be a major pain in the ass to set up in the first place, but once they are they run like a dream, though will need adjustment with coral growth of course but its usually easy to do, as growth is consistant so usage goes up in at a pretty steady rate (though somewhat exponential). If you use broken coral skeletons as your media you don't have to dose traces either as the skeletons have alot of them already in it. Generally I've seen little change with pH, but you may need to add buffers to the display keep it consistant, but generally the acid (carbonic) is very short lived as it is considered unstable, so it will either evap out or get used by plant life as fuel (once it converts back to CO2). So unless there is a large failure in the system it is unlikely to cause major damage. Here is a link on how to use/setup one http://reefkeeping.com/issues/2002-05/sh/feature/index.php (don't be surprized if some of what I said is contradicted here, its been a wile since I read it/used one lol). This link at the bottom actually has some excellent tips on how to keep acidity out of your display, or at least how to minamize it (namely using airstones at the drip outlet and stuff like that).
Oh and btw that is actually a sick recactor setup, I've always DIYed my reactor chambers though to save cash.
Oh and btw that is actually a sick recactor setup, I've always DIYed my reactor chambers though to save cash.