The Tetra Test pH accurately and reliably measures the pH level of aquarium and pond water. The pH level in water is one of the most important criteria in the balance between acids and bases. If this balance suddenly changes, fish and microorganisms, like plants, react extremely sensitively. Therefore, the ideal pH level should be between 6.5 and 8.5, depending on the type of fish being kept. It offers good long-term stability and a high range. Suitable for freshwater and saltwater aquariums and ponds.