Ultra provides excellent long-term protection from shell and weed fouling. Ultra contains a very high loading of cuprous oxide and uses Biolux® technology to block slime. Ultra is recommended for use wherever the fouling challenge is severe, and can be used in fresh, salt and brackish water on fiberglass, wood and properly primed steel boat hulls and parts. Even though Ultra has a very high loading of cuprous oxide it has excellent color stability and resists changing color at the waterline.