Coralline Algea fading away. Cause?

i also had this problem when using purple up. It raised my alkalInity too much and had the same results you describe. Test your alk and if its too high do a wc,

 

IME, coralline is hardy. It may fade but it always comes back. Many people try to control the growth, as it can become a nuisance.

 

+1

I heard many cases where people scrape it off the glass because it can use great part of the alkalinity and calcium supplements. I will probably only leave this coraline in the back glass only and whatever rocks it gets on. It's also growing slowly but steady.