If you are keeping saltwater fish only follow the ideal parameters in the first chart. If you keep saltwater fish with invertebrates like crabs, snails and shrimp your can follow the first chart just keep your nitrate levels less than 10 ppm. 

If you have a saltwater aquarium with live corals it is important to follow the recommendations on the next chart. Regular water changes will help keep most levels in range although a living reef with hard corals typically requires additional calcium, carbonate and magnesium supplements.