[Delphinus]

Don't get rid of the rock.

How old is your tank?

Unfortunately, it's not uncommon to go through a few different plagues during a tank's "settling in" period. Although a tank may be "cycled" within a matter of weeks it's not truly hit a sort of equilibrium/steady-state until a few months in and until then you can have a plague of cyano, a plaque of hair algae, probably a bunch of other things that make you think "This sucks! What am I doing wrong!" and yet you're not doing anything wrong, and if all else is well then they should pass.

However, in general, cyanobacteria blooms result from a high nitrate level, thus anything that helps lower nitrates will help keep it in check. These include, increased water movement, increased skimming, growing/pruning macroalgaes such as caulerpa (or even better, chaeto), reduced feedings if overfeeding, etc. In a new tank it could be as simple as the bacteria populations required to reduce nitrate simply haven't reached the tipping point yet.

If it gets *really bad* there are treatments such as "Red Slime Remover" and they do a bang-up job, however if the root cause of the cyano is not addressed, it will return.

Also, sometimes cyano can indicate old lights. In my first tank that was lit only by 4x40 fluorescents, I could always tell when the actinics hit six months (literally, to the day).