Making reef rock

[Logistikon]

Hi. I'm excited to make my own reef rock. Can I use powdered calcium carbonate instead of sand, or will that interfere with the chemical reaction in the cement?

My mix would be, 1 part calcium carbonate powder, 1 part limestone sand, 1 part coarse rock salt, 2 parts white cement.

I'm also going to attempt to embed some purple barnacles in there.

Hope to hear from you!