We will need more info.
Tanks Size, Tank Parameters, Type of Lighting, Power of Lighting, Location of Xenia in the tank, Low flow area, high flow area?, What else is in your tank?
As for the Xenia's, I put mine it, and noticed growth within a couple of weeks. I am runnin 4wpg, and have a very stable tank.
As for coraline, You need to have your tank parameters PERFECT before you will starting noticing coraline growth, Once it starts, as long as you keep your tank stable with all the right parameters, it will begin to grow pretty rapidly.
What's your magnesium level? What's your Calcium level? PH? dKH
Purple up is NOT the cure all for coraline algae as some think. I too purchased purple up thinking it would help, but it didn't untill I found out WHY my coraline wasn't growing. I was low on magnesium, thus no matter how much calcium or purple up I added, nothing would happen, but as soon as I got my magnesium up, my tank just blew up with coraline, and my calcium stays right were it is suppose to be.
Answer those questions, and we will be able to help a little more!