I ordered 25# of Marco a month ago and put it into a brand new 60g reef I just set up. I rinsed and cleaned off the rock a bit, but did not cook the rock. I figured since this was a new tank, I would just cure it in the tank like I do with my LR. NOT a great idea... For those of you in the same situation, do not treat this MR like you would LR. The smell and filth that comes off is something else entirely. The water turned milky white and stayed that way for almost a week (even with multiple water changes). And as other's have mentioned, the smell was bad too. It was NOT the same smell as uncured LR, but something much worse. The wife was a little upset at me because it smelled up our living room quite a bit...
I took the rock back out and cleaned it thoroughly and did a 95% water change to get all the crude out of the new tank. Decided to just start over (for the most part).
I must say; however, through this mess, I had the chance to really see how well my new Octopus skimmer works. This is a brand new skimmer, I just purchased for this new 60g tank, and boy did it work well. It pulled some gunk out that was just shear nastiness. That stuff coming out of those MR is just nasty, nasty stuff...
I learned two important things here... 1) CLEAN your Marco rock well & do not treat it like you would LR. 2) Octopus skimmers ROCK for the money.
Cheers,