Red Scale on glass of Saltwater Aquarium

Question
I have a 22 gallon nano cube aquarium.  I st it up with live rock and live sand and it has been in operation about 6 months.  I have 3 fish, about 10 snails, 5 hermit crabs, and skunk shrimp.  All seem to be doing well, except I have lost a few snails.  

Over last two months, a red scale has developed along back black plastic divider in tank and then moving onto glass and everything else in tank.  It is virtually impossible to scrape it off with anything short of a razor blade.  fish seems to still be doing fine.  Can you tell me what it might be and how to get rid of it?

Answer
Hey Tim

If its dark red, its cyano. its normal for your tanks age, and in a month or two will go away. you can do extra water changes and feed less to keep it down in the meantime

if its pink, its coraline, which is desirable and not a bad thing. Im thinking its coraline if youre finding it hard to scrape off

good luck!