You don't need purple up or any other chemical to get coraline algae. My tank did start out with a few pieces of live rock that had coraline algae. I started with 50 pounds of LR
and 50 pounds of base rock (marco rock which is almost white)., After about 3/4 months all rock in the tank was purple. At that time I did not dose anything. Over the last month I began dosing Kalk
into my tank. Now if I put a piece of base rock in my tank it will be completely covered in coraline algae and totally purple in a month or so. I don't know if it is because of the Kalk
additive or because the tank is healthy and full of coraline algae.