Coralline algea going away

[Ruth]

Until about a month ago I was constantly scraping coralline off my glass. My back wall, powerheads and overflow walls were covered in it. Now it has all turned green or else just gone away - it's hard to scrape but not like coralline that chips off. I am not getting any new growth on my tank walls. I have made 2 changes in my tank in this time. The first was to put my calcium reactor on line and the second was to change my bulbs to Giesemann 13000K (my previous ones were Coralvue 15000K). I still have lots on my live rock and it is not turning green or fading. My water tests at:
Ammonia - 0
Nitrites - 0
Nitrates - 5-10
Calcium - 480
Alk. - 3.2 meg/l
Mg. - 1350
Ph - 8.2 - 8.5

Any ideas? Not that I particularly like scraping coralline off my tank walls but I am concerned that soon my rock will go the same route.