Coraline Algae Dying - Help!!

[Marty123]

I have a 55g tank that has been running for 9 months. It contains approx 30kg of LR. Everything has been fine until recently. The Coraline Algae (the purple stuff) on my LR has started to go white and flake off. My Ca levels are a little high if anything at around 490ppm and the Kh is ok too.

Please can you point me in the right direction!

Thanks

 

[seafan]

what about temp and water flow? coralline is very sensitive to temperature change, and like alot of water flow.