An important thing to bear in mind is the pH level you will need to achieve within the calcium reactor to dissolve the medium. In a typical reef tank with pH 8.2, the calcium carbonate is supersaturated, and it tends to precipitate onto other fresh calcium carbonate surfaces. At typical reef tank calcium and alkalinity levels, a pH of around 7.7 or less is needed inside the calcium reactor for aragonitic media to begin to dissolve (Holmes-Farley 2002). Generally, most people get good results dissolving aragonitic media inside the reactor at pH 6.5 to 6.7, but be aware that some of the harder CaCO3 media, such as those made of calcite, will require an even lower pH to dissolve easily. Dropping the pH too low inside the reactor (in my experience, this is less than 6.5 for aragonite) often leads to the media turning into fine particles that slow the water flow through the reactor.
