I had some red algea in my tank that was a result of my adding too much calcium too quickly. Are you using a calcium supplement? Have you tested for calcium in your tank? If you do and it tested high, I'd suggest water changes to dilute it.
Jim
There are a few products out there that are effective at getting rid of red slime. I used something called red slime remover a while back and have never seen it again. It is safe for inverts.