Ive just wrote this in another post earlier...
I had OceanRock in my old tank but i wouldnt have it again.. with it being white, it turned yellow (yes, not green!!, but yellow lol) with algae within a week or so. I really didnt like the look so i had to change them.. i got large brown river cobbles from B&Q and i love them, they look really well (alot cheaper too).
You can scrub it off but itll only grow back.. if you really dont like it, then your best changing them for darker rock.![]()