+1 on the idea, not the removal. You can tell the difference by brushing it with your hand. If it comes off really easily and in a mat, that's red slime algea (cyanobacteria). If not, it's red coraline and you're good. To get rid of the cyano, you'll want to upgrade your flow rate and possibly cut down on your lighting schedual. What kind of water do you use? Do you have a phosphate test?