Sounds like a nasty algea. Bad water quality. Cyano is red, or I'd say thats what it is. You could syphon it out. But if you don't clear up the water quality, its coming right back.
new tank? end of the cycle? = diatoms. Don't do anything, just do the usual maintenance you would do and it will eat it's self right out of your tank. it will grow thick and then just dissapear.