If you're going to continue with the PurpleUp, even with the comments folks have made here, please at least go out and get a Calcium and Alkalininty test kit, and use them. If you get your tank chemistry out of whack, you'll be cussing yourself later on.
As Melosu58 noted, you *may* be able to get the calcium levels you need with just your normal water changes. Personally, I can't because my fresh salt water only mixes normally to about 360ppm Ca
. BUT... the point is, I *know* what my Ca
levels are in my tank and in my new fresh water I'm putting in. Without knowing that information, you can't really make a decision on what you need to do. Your new salt water may have 400ppm Ca
in it to start with... in which case you don't need to add anything to get coralline algae to flourish.
Take a read of this...
It's my favorite article on the whole Ca
issue. You should see how the two are interdependent and messing up one can mess up the other. Messing with Alk
can have bad effects on pH. And after your pH starts swinging all over, you're going to see problems elsewhere.
I think one of the best pieces of advice I've gotten off this board so far is that if you're going to add supplements to your tank, then you should at least test for whatever it is you're adding. If you're not testing, you don't even know if you need the supplement to start with. Just because your LFS
sells it, doesn't mean you need it!