New to the world of saltwater, need help!

[hrlbaker]

I have a 55 bowfront saltwater tank that I set up about a month and a half ago. I purchased 50 pounds of live rock online and it has been in the tank since week two. Also has 60 pounds of live sand. I haven't had many problems with the rock, a little fuzzy mold/algae stuff at first (took to petco and the associate had no idea what it was) but I got three hermit crabs which took care of that. My levels spiked once at the beginning but have been normal since then. I have not added any fish. Anyway...I recently got promoted through work and have to move an hour away (perfect timing, huh?) so I am tearing down the tank and taking steps to preserve the rock in bins with heaters and powerheads. On one of the rocks, it is black and has a strong unpleasant smell to it on the bottom where it was in the sand. What is it? Did I just get a bad rock? Is there anything I can do to fix it? And once I get my tank back up what should I do to avoid this happening to the rest of my rock? Any advice would be helpful and I appreciate everyone taking the time!

 

[Fishguy2727]

Stinky and black (most likely smells like rotten eggs) is toxic anoxic bacteria that are producing hydrogen sulfide. This happens when no oxygen gets to parts of the rock or sandbed. This is different from anaerobic denitrifying bacteria which are beneficial. Those bacteria live where there is almost no oxygen, but just enough to keep the hydrogen sulfide producing bacteria from growing. Flow around rockwork and not having too thick of a sandbed will help avoid this problem.