Whats on my rock

Just trying to get some help identifying what's growing on my rock and if its good or bad, normal or abnormal.
Its pinkish purple color mostly, but there is also some green in there too. Doesn't really feel slimy at all. There is no real length to the strands, just more like an even covering. Its not a real heavy covering, but it is slowly getting more dense. It's all over what was the dry rock, and some in the sand. I'll try to include a pic, but its not the best. " />
[img]http://i19.photobucket.com/albums/b187/darobinson/P1010078-1.jpg?t=1274836842

 

doesn't brush off too easily. Seems to be stuck on there pretty good.
tanks is only a couple months old. occupants are a damsel a couple clowns, crabs and snails.
PH ~8.2
ammonia, nitrite 0
nitrite 5-10
that's all I can test for ATM.

 

tanks been up for 2 months or so its a 40 long. lights are 260w PC fixture with dual daylight and dual actinic bulbs. for flow I have a 750 koralia evolution, a 425 koralia nano and my HOB skimmer that I am not sure of the GPH

 

is there an easy way to tell the difference between the 2?

 

LOL. I tried that. Some of the pics of cyno look like my issue others don't. And some pics of diatoms look like what I have while others look completely different. /DesktopModules/ActiveForums/themes/_default/emoticons/confused.gif I adjusted my lighting cycle so they are on less each day and I backed off the feeding a little. I guess we will see what happens.

 

update
Cut my light cycle a few hours and reduced feedings and it appears to have helped. Seems to have stopped spreading and is even starting to thin out in some areas.