The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
I would lean towards coraline. Is it on the sand, do you see it forming on the glass or anywhere else besides the rocks?
Like you said it looks rather spotty and I think that if it was cyano that it would be more sheet like and covering a bigger area of your tank! JMO though.