Purple up only contains what your salt mix does pretty much, it's mostly calcium. Now, some people will say it's useless. Me, I tried a test with 4 tanks in my house and to my amazement I actually saw more coralline with the tanks that I used it on. I did this test over a few months and dosed it once a week. Your results may vary......LOL
I also have intense coralline growth in a tank that has not seen purple up so it's dependent on your tanks parameters and a myriad of other things. There's no instant purple if thats what you were hoping. lol