CaribSea Purple Up has a unique dual method approach to coralline algae acceleration. Approach #1 Ionic calcium: Immediately raises dissolved calcium levels in your aquarium water. Approach #2:Ten micron aragonite: Targets the live rock surface, where it dissolves in situ (in place), delivering calcium, strontium, magnesium and carbonate right where it is needed.

About Purple Up, from the CaribSea.com manufacturer Web site:
Purple Up uses a unique dual method approach to coralline algae acceleration. This approach is so unique that Purple Up has been awarded a US patent (US patent No. 7,565,883). It contains ionic calcium; which immediately raises dissolved calcium levels in your aquarium water. At the same time Super Sea Calcium (a 10 micron aragonite powder derived from natural seawater) targets the live rock surface. This dissolves in situ; delivering calcium, strontium, magnesium, and carbonate right where it’s needed. Purple Up also replenishes iodine; an essential element for coralline algae tissues that quickly becomes depleted in closed systems. Purple Up is not a fertilizer, it does not promote the growth of nuisance algae.