Is this a shell problem?
I've had my RES for less than a month, and lately I noticed blackish stains around his scutes. From what I've read in the forums, shell rot should be white in color. I've tried scrubbing with a soft bristle toothbrush but it doesn't seem to remove the black "stains".
Can anyone advise me on what the growth is, and how to nurse it away? I've included some pictures below:

Can anyone advise me on what the growth is, and how to nurse it away? I've included some pictures below:

