... long name just gave great advice. That is cyano
, and I have no idea about the stringy stuff but better safe than sorry. Beautiful tank though! Two power heads may not be enough. Try adding a propeller type circulation pump.
On real reefs, the erratic currents can be amazingly strong so you're not likely to have too much flow, so long as no pump is aimed directly at a coral.
Dont worry, this is nothing you can't handle. You're off to a better start than many!