Yep it's absolutely red slime. Had this problem about a month ago. You can suck it up with during water change but will come back within a day or two. I went to get LFS and they gave me red slime remover by a company called ultra life. Within 24 hours it was all gone! And I had a lot more then you did. It says it could take two try's or even lower your ph, but I never had any problems. Do a couple small water changes, even though you can't see it, it's still in your tank. Clean filter pads, etc.