We used Type II portland cement and crushed oyster shells. We cured is in buckets for about a month and a half until the PH dropped to about 8.0 and then transfered it to saltwater in our new tank last spring. After that we didn't have any PH issues, but for about the next 2-3 months the measured Ca levels were greater than 700ppm. Since about last May the Ca and PH have been maintained at reasonable levels. Since that time we have had on and off algae issues and it has been impossible to keep any SPS's alive. The LPS's that we have had either stagnated or slowly died. During this time ammonia, nitrite, nitrate, phosphate, Cu have all been at unmeasurable levels using Salifert test kits. We have also had some live rock in the tank, that was supposed to seed the DIY rock. What I noticed was that there was much more algae growth on the DIY rock, essentially no coralline growth.
About two weeks ago we finally gave up on the DIY rock and removed it all along with the 2" sand bed that we had. We noticed an almost immediate improvement in all of the corals in the tank. The Hammerhead that was barely extended now extends 2-3", our blastmosa has sprouted a new head etc.
I'm not sure what was going on, but things are much happier without the DIY rock.
Bob