Well Rule #1 - Never add anything to your tank without being sure your tank is short on that type of chemical
Purple up primarily adds calcium to your tank, so if you're Calcium is fine then you don't need it. If you're Calcium is low then you just need to add Calcium. Purple up is just a fancy name for Calcium buffer
Purple up also doesn't add Coraline to your tank, it only helps it grow so if you have no Coraline algae currently it won't help you. You're best bet is to get a Live Rock with Coraline Algae growing on it and use it to seed your tank.
Also if you're Phosphate levels are high then it inhibits the growth of Coraline.