It is Cyanobacteria. You are going to want to siphon out as much of it as you can. You will also need to find the source of the nutrients that it is feeding off and make sure you have enough flow in the tank to keep it from settling. If you make sure you have good flow, cut back on feedings if you are feeding, and siphon it out when possible it should eventually go away.
Another thing to consider is how old are your light bulbs and is it time to replace them due to reduced PAR.
Good luck in your battle with the
red slime.
Chris 
