Yeah, actually the cement will "cure" harder in freshwater. It makes the cement real hard. I have been doing it for a while. After I get the pH level consistantly at 8 or below I put it into a saltwater mix and circulate the water. It doesn't even have to be sea salt. Once I get the pH stable in the saltwater, I move it to my final curing tank whick consists of some regular live rock with corline on it. I am trying to get the coraline to grow on the "cement" rock. I have got it once so far. It started growing about 4-5 weeks after I put it in. I am dripping calc into the curing tank but not a lot. I use the water changes mostly. Once I am convinced it (the rocks) are OK I am going to put one piece at a time into my tank and watch the water quailty daily until I am sure it's OK.
125 Gal-35 Gal Wet/Dry-Tetra-Tec PF500 HOB
(3) AuquaClear 301 Powerheads-600 GPH
Automatic Tempature Controller
5-6 Inch Sand Bed-200+ lbs of LR