I beleive this is the stuff that does need to be soaked/cured before use, due to PH issues. There was a disclaimer during the video, to make sure ph held stable, and salinity held at 0 during the soak.
i love it when people answer the questions for me........ yes it dose need to be soaked in fresh water of about two to three weeks and if it was me i would change the water a few times as the cement has ph properties that need to be removed. the salt and oyster shell is there to keep it porous. oyster shell will later help with ph as it is calcium based. the big question have i made this my self...... no i have not but i saw it and new it needed to be shared.
My tank is small and i do not need any more rock but i would love to see you guys make some and post your xp for us.
I have made about a 100lbs the same way. The best way to cure ur rock is to put in ur toilet water tank so every time u flush it gets rinsed. I let mine stay in the tank for a month and never had any problems. Good luck!