Reactors Information

Useful especially in bigger reef tanks, the calcium reactor reacts your water with CO2 and calcium to maintain constant calcium levels in the tank. Calcium is an important and essential part of your testing and you should maintain levels around 480ppm. The downside, is that these reactors can be extremely expensive, most costing between $700-$900.
b) Biopellet Reactor
Biopellets are a semi-new thing in the reef hobby. Biopellets are basically small plastic balls that the water is passed through. The idea is that these pellets will induce nitrate eating bacteria, and will help keep the water clean. Biopellets will dissolve over time, and you will have to replace them.
c) Carbon / GFO
Carbon is an awesome way to keep your water looking great. I run ROX carbon in my tank, and it keeps the water clean and absorbs more of that bad stuff we were talking about earlier. GFO stands for Granular Ferric Oxide, and that absorbs phosphates from the water. I highly recommend a Carbon / GFO reactor, it has made a huge drop in phosphates and nitrates in my tank.
d) Kalkwasser
Kalkwasser is a german word meaning lime water. Kalkwasser is a powder that is stirred constantly in what is known as a Kalk Reactor. Kalkwasser helps maintain proper ALK and pH levels in the aquarium.
e) Phosban / Zio
These are optional reactors that rid your tank of more phosphates and help keep magnesium levels steady. I dose my tank (I will talk about that next) so I do not use these reactors.