As Rick said, Purple up is a concentrated Calcium supplement, which is what coralline uses to grow. Its also what corals require to grow. Dosing a calcium supplement without testing for calcium levels can result in a surplus of calcium, which could throw your calcium, alkalinity and magnesium levels out of wack, causing a negative effect like marine snow to occur in your tank. First rule of saltwater aquariums is to never add anything to your tank that you are not testing for. Premade salt mixes contain levels of calcium, alkalinity and magnesium in the required concentrations.
"Listen to some of these guys talk, and it's like they were born from their momma's belly with a fishkeeping encyclopedia in one hand and an API kit in the other" (unrevealed).