Okay, so after my tank crashed, killing everything other than a few hermits, snails and a yellow tailed damsel, I decided to start over from scratch. As I was scrubbing my live rock with a toothbrush under fresh water, I noticed some white areas under the bottom side of some of the rocks. It smelled strongly of sulfur. I tried scrubbing as much off as possible, but couldn't get it all off. Does anybody know what this is? Should I use a hammer and chisel to chip off these pieces, or leave them alone?