Coming from a guy who is only been using calcium reactors for a couple of years, I can dumb it down for you. Basically, you have a cylinder filled with dead coral skeleton that you are circulating water through. You slowly adding CO2 to bring down the ph level in the reactor. Lowering the PH in the reactor dissolves the coral skeleton therefore, creating a mixture of dissolved coral skeleton (effluent) that has everything in it that the coral originally needed to grow (cal, alk, mag, etc). Then, you slowly add that dissolved mixture (effluent) back to the tank via a peristaltic pump. Easy peasy.
You just have to purchase everything which is a pretty large start up cost but, is worth it down the road. To answer your question, yes you can mess up a tank pretty bad by not dialing it in right and over dosing the tank.
In my opinion, the easiest way to dial in a calcium reactor is to start with a slow drip rate back into the tank and adjust from there. Some people with tell you to adjust the Co2 level but, in my opinion, keep the reactor at a steady PH and adjust the amount of fluid (effluent) dosed back to the tank. If it gets to the point where you are dosing a lot, that's when I would adjust the PH and make the effluent a stronger mixture.
Hope this isn't too geeky of a response.
Good luck!