He still needs to cure the Marco rock. There is still quite a bit of dried, dead thingamajigs in the rock to decay once it is rehydrated.
Don't cure this in your new tank or you will see **** yellow water :lol:
Use a rubbermaid or brute trash can and fill with saltwater. If you have a existing tank, then do a water change and use that water, if not, then use newly mixed saltwater.
Best if you can keep the water moving with a powerhead and even better if you can put a skimmer on.
Change out the water every 1 to 2 weeks and you should be ready to rock in about 6 weeks.