I guess between 1 and 3 feet across? I hate the look of stacked rocks so wanted to just make 2 or 3 islands composed of 1 or 2 rocks eachIf I were you I might contact a lfs to see where they get their saltwater supplies from and move up the chain. Or you could ask an aquarium where they got their rock from. How large we talking about measurement wise?
I think if i dont recall it wrong that its with filling the fiberglass to. On the epoxy they used i think its recommended to put 0.5mm per layer of epoxy then mix the last layer with black pigments and finish it of with black top or gelcoat. Me personally find it easier to build with pondliner insteadIs that including or not including the epoxy required to fill the glass?