Two Little Fishies STAX Rock, 5 lb, is a flat, porous oolitic limestone for building layered aquascapes in marine aquariums. It provides a stable structure and will not introduce pets into your aquatic environment. Use with Two Little Fishies STIX Cement to make open, gravity defying structures with lots of horizontal surfaces for attaching live corals. Use with Two Little Fishies STIX Cement to make open, gravity defying structures with lots of horizontal surfaces for attaching live corals. Use with Two Little Fishies STIX Coralline Red Cement Mortar System, Two Little Fishies AquaStik or Two Little Fishies CorAffix to create a base for large coral frags. Each box weighs 5 pounds. Pieces vary from box to box. Most of the pieces range in size anywhere from 3" x 4" to 4" x 6".