Is this anything specific?

[AdamW0611]

I have had these rocks in water for about 5 or 6 months, in a 75 gallon for 3 months and upgraded about 2 months ago. It won't come off the rocks and none of my snails seem to eat it. I thought it was turning black, but the more I look it almost seems a dark purple. I do have Coralline a few Trochus snails, but have no idea if that's what I'm seeing on the rocks, or if its a problem. Any ideas? When I upgraded the tank I used all new sand and water, I think the brown around the bottom of the rocks is diatoms from everything being new again

 

[Gareth elliott]

Looks like normal new tank algae, the purple being coraline. There is always some locked nutrients in new rock(usually phospahte). That algae is starting here because the food source is there. If dislike a hard bristle brush and a water change after will help with the green type.

 

[AdamW0611]

Looks like normal new tank algae, the purple being coraline. There is always some locked nutrients in new rock(usually phospahte). That algae is starting here because the food source is there. If dislike a hard bristle brush and a water change after will help with the green type.

Ok, I don't mind it, I actually like the color better than the white rocks. I Just wanted to make sure I wasn't ignoring a problem. I did buy a brush just to scrub it when I moved to the bigger tank and it didn't come off at all.