I have been using a product called "Quikwall" its made by quikrete. This stuff does not require a ph "kure" it is formulated for potable water holding facilities and such. I will post some pics of my diy rock background and frag plugs. You still use the crushed oyster shell or whatever you choose to use and still have to cure it so it hardens and then after a couple days when it has reached fairly decent strength just give it a good soak for a few min or hours and rinse to get all the loose stuff out and its ready to go!! The only negative part of the quikwall is it contains small strands of fiberglass in the mix, but it can be removed without changing products performance.
Disclaimer: I will not be responsible for anyones actions but mine! Please double check your ph levels of the product before installing in your tank Good Luck and Happy Reefing!!
Disclaimer: I will not be responsible for anyones actions but mine! Please double check your ph levels of the product before installing in your tank Good Luck and Happy Reefing!!