Coralline algae turning green

[Erik L]

Got a call from my brother, he said it looked like his coralline algae on his rocks appeared to be turning green. I asked if it was green hair algae and he seemed confident it wasn’t. He said a few weeks ago he turned his light cycle down to about 5 hours per day and said his kh is slightly low at 7.5 but everything else seems to be ok. Here’s a pic:

any thoughts?

 

[Scrubber_steve]

when i see coralline algae take up on a bare spot in my tank it usually starts off a green color before turning pink/purple.
There apparently is green coralline. But I don't know if that is what's happening in your case?

 

[Txplicit]

That doesn't seem like coraline algae. Ask him to blast it with a baster or scrape it. Does it come off easily? Is it kind of slimy in texture?