Coraline algae will grow with time and light. Patience.
If you want to go a faster way, as long as you have some coraline algae growth on your LR, you can use purple up. Good stuff IMO, some people will disagree with me, has worked well for me.
Niño
How high is your calcium ?
If you read the bottle IIRC it says if your calcium is above 400 ppm dont use Purple Up.
I'm pretty sure it's just calcium.
Just tested my ca the other day and it's at 420ppm, I don't dose it anymore, it's a good starter for people that want a boost. Like I said, others disagree, I have nothing negative with the product or the way I was dosing when I first used it.
Ok, never heard it called a "card" before LOL