Need a little help, when I setup tank some of my live rock got buried beneath the DSB, I didnt think anything of it, but as I have been moving rock around, i discovered the rock that had been buried has turned black, and smell terrible when I took it out of tank. What exactly happened and what should I do, I move all my rock to "holding" bins and moved my fish back into 10 gallon QT tank. It seems all the rock that was under sand is like this.