Went on vacation, left my fish in the care of some one I trust and knows some fish care. I came home and one of the bowls had black slimy stuff in the bottom of it, and the fish decoration I have had for years was covered in it. Not sure what it is or how it got there. I have left my fish in their care before and was only gone for a week. I trashed the decor and the rocks, but what do I use to safely clean the bowl? There is still black stuff in it Bleach water? Vinegar? Please help.