There are many types of reactors for the reef aquarium and they all incorporate unuiqe features and specifically designed for different medias.
This most popular is the aquarium carbon and GFO reactor. This is a simple upflow reactor designed to force water through the two medias so they can remove undesirable polutents from the water.
The calcium reactor is designed to dose calcium and alkalinity to the tank in the form of ionized calcium and carbonate. It does this by using carbon dioxide to melt old coral skeleton or other calcium carbonate media into solution and then drip it into the tank.
The biopellet reactor is used to tumble your biopellets and keep them free flowing. The bio pellets will reduce both nitrates and phosphates
The zeovit reactor is designed for the zeovit system which keeps nutrient levels ultra low. The ultra low nutrient levels results in reduced algay growth and more colorfull corals. It is recommended to also dose additional aquarium additives and supplements to feed the corals.
The kalkwasser reactor is designed to mix calcium hydroxide / kalkwasser with water and dose it to the aquarium. This is often part of an auto top off solution and fed with an aquarium dosing pump.