Cyanobacteria

If you wish to "know your enemy" Albert Thiel posts this lenghty article on marine cyanobacteria: http://www.netpets.org/fish/reference/reefref/cyanobacteria.html

But the core of it is that cyanobacteria will thrive where dissolved organics, nitrates, low water flow, and poor lighting are prevalent.

So to discourage slime algae try to feed a little less, increase protein skimming, do more frequent water changes, better positioning of powerheads, and better quality light spectrum (not necessarily intensity).

I agree with squid.

But I also used something called a poly filter. I cut a piece of it and stuck it in a hob and hung it on the back of the tank. It strips harmful organics, ammonia, heavy metals, phosphates and any meds (at lest that what the package says). It got rid of the slime within a week. But be warned, my critters living onmy LR died right about at the same time, so maybe not all the organics that were stripped were "harmful". I would suggest trying it for a few days, then backing off and see how the tank reacts. Again, I agree with squid on the lighting, feeding, and wter flow.

A low pH can create a bloom too.