Instant Ocean Holdfast Epoxy Stick (4 oz) The HoldFast Epoxy Stick has superior bonding ability that allows you to create steps, caves, cliffs, and walls for aquarium animals to enjoy. It bonds all types of materials from rocks, to corals, to slate, and many more. HoldFast Epoxy Stick is non-toxic to fish and invertebrates and is great for use in freshwater or saltwater.