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If I understand it correctly, coraline is a great thing to have because it is a plating algae. This makes it hard for microalgaes such as hair and bryopsis to take hold on. It is also pleasing to the eye, as it comes in reds, blues, purples, pinks, greens, grays, etc... The purple is my favorite, but I seem to be cursed with green, pink, and dark red....
It lives on calcium, so if you are getting good growth, the levels or calcium and alk must be pretty good.
I have heard that in addition to being eye pleasing, coralline also helps in the nitrification process, reducing nitrite and nitrates. A LFS employee, an older gentle man, told me about a navy meteorologist (forget his name) who couldn't keep SW fish alive for more than a few days. One day after a storm there was LR washed on to the beach and, liking the colors and myriad life forms, he added it to his aquarium. Viola, fish would now live for weeks at a time. Hence the birth of LR in the aquarium!