Coralline can grow on powerheads, heaters, skimmers or any equipment within the tank. These items which can be removed from the tank. They can be soaked for a few hours in a solution of 50/50 water and distilled white vinegar in which coralline algae is easily dissolved.
I use a bucket which is specifically set aside for using with items from my marine aquarium. This way I know that no household chemicals are present which could potentially be hazardous to marine life.
Once they have been left to soak for a few hours all you need to do then is brush it away with a toothbrush or any other stiff brush.
Depending on the thickness of the coralline algae, you may need to repeat the process a few times. Or leave them soaking overnight to give the solution time to fully dissolve the coralline algae.