Man am I glad I picked up that rock, that was a killer deal! $60 got me all the rock you see in the tank, and three partial bags of coarse sand, most of the rock has already had an acid dip, but it will all get a good soak regardless. I'm thinking I have at least 25 pounds, the larger pieces are very open and porous- and quite light for their size. I'll have to play with stacking, and may break some up to build my structures with some PVC framework.