[Reefmack]

Hi Laurent - it does indeed look like pink/purple coralline on that center rock. The more you get of the coralline the less places that algae has a chance to grow, but it takes time to get a lot of coralline.

One thing I've always wanted to do, but haven't yet, is to somehow attach the bristle end of a toothbrush to my siphon. I think that would really help to be able to scrub algae off the rock and at the same time have it siphoned out. I'm surprised someone doesn't sell anything like that. One of these days I'll get to it, but I think it would really help in cases like yours and Rue's. I still get a small patch of algae once in a while and it can be difficult to pull it off (too slippery) but I think a stiff brush would help.