Coralline algae eb & flow

To cycle my tank a couple months back, I used some really mature LR (about 1/3 of my LR). Pretty much covered with coralline. When I first put it in the tank, it immediately started going south. Bubbling and bumps on the surface, and it turned REALLY white. After reading up a lot on it, I was aware that the changes in conditions and lighting probably made this happen, and that over time, it would bounce back and return to its original, glorious purple/pink state.

Well, that happened! It came back and looks even better than when I got it, once my water quality went up.

However, despite constant conditions (closely-monitored water levels, and light timer, rock hasn't moved), it's now gone back and forth from turning more white (not nearly as much as before, but definitely noticeable) to more purple again a couple times. Is this to be expected? Is there just a perpetual cycle of dying and regrowing that I can never control?

Sorry, this may seem like a dumb thing to be concerned about, but coralline is something I'm really really interested in, so I'm wanting to see some growth progress, which I'm seeing, but I want to be sure there isn't some factor I'm missing here.

Tank: 9-gallon cube
Ammonia: 0
Nitrite: 0
Nitrate: <5
Phosphate: <.25
Calcium: 420