Well, for coralline, you need Ca, Mg, low nutrients, and Alk. If you're using Purple-Up in lieu of the other necessities, I'm afraid you're inevitably setting yourself up for failure. The reason kalk is so popular is not so much it's ease of use, but it's because you need to top-off your tank anyways, why not use something that 1) Adds Ca&Alk 2) Raises pH 3) binds phosphate? You can use other additives, but the required parameters are there. You can invest in a Calcium Reactor which will also supply the required elements. I guess bottonline line is, once you undestand what is required for coralline to grow, and which additives do what to your system, you can make better choices as to what methodogy works best for you.