Just so you understand this stuff read this
Cyanobacteria
What is it?
Cyanobacteria (aka red slime algae) is a photosynthetic prokaryotic bacterium that typically grows in films, commonly with hair-like projections that may resemble hair-like algae, that is shiny, almost velvety, red in color.
What causes it?
The most effective and simple way to treat cyanobacteria begins with understanding what causes it. Three major factors are going to influence the growth and proliferation of any algae or cyanobacteria growth: nutrients, circulation, and lighting. The most common cause of cyano bacteria is simply an accumulation of debris/nutrients in an area of the tank that is not receiving adequate circulation. For example, you may notice it growing on the sand bed right under the edge of a rock that blocks water from blasting nutrients that lay there up into the water column to be removed by your filters. It also could be that their is a spot in your live rock that isn't being hit with enough flow or just happens to be shaped in way that favors debris settling there.
Treatment
99% of the time cyano bacteria can be treated very simply by just making a few adjustments in your tank. You either need to move your powerhead so that more flow is hitting the area where cyano is growing, or you may need to add an additional powerhead or form of circulation to hit that area a little harder.
So to treat it, I'd recommend when doing your water change to take a gravel vacuum or piece of airline hosing and carefully try to suck up as much of it as you can (also try to suck up any loose debris that could feed it again). Then change the flow up in your tank so that the area is being hit a little more aggressively.
IT REALLY IS THAT SIMPLE. I PROMISE.
There is really no need to spend money on fancy chemicals that may kill it, but will not actually address the cause of it. If you do not address the cause, it WILL keep coming back and you will keep spending money on more fancy cures.
The use of any medication/chemical should always be a last resort anyway.
SHOULD YOU CHOOSE TO USE CYANOBACTERIA REMOVAL PRODUCTS USE EXTREME CAUTION!
No joke. Typically the main ingredient in these magic pills is the antibiotic marycin which can be very dangerous if not used correctly. READ THE INSTRUCTIONS VERY CAREFULLY. Marycin may lower the oxygen level in your tank and change the pH. If you use marycin I'd recommend keeping an airstone w/ course bubbles in the tank during treatment. You may lose fish if you don't.
Products such as phosphate removers/reactors, chemipure, etc again will only temporarily fix the problem and/or will be reliant on your continued use of the product. If you want it gone for good at zero cost, use the method described above.
AGAIN...do not use these products unless absolutely no other natural method will work. I guarantee though that if you just play around with your water flow and make sure you have a filter sucking up all the crap that is dislodged, it will start to go away on it's own.