Most people who pass the beginning stages of reefkeeping start to think their system is in need of a calcium reactor. For most larger tanks, it is a must have as daily dosing can become monotonous. A calcium reactor can eliminate the dual dosing of both calcium and alkalinity however, calcium reactors can be also be expensive and require a fair amount of space as well as an adjustment period to find that perfect setting.  In the long run they can be just the thing to keep your reef happy and healthy.