The Tetra Test Nitrite NO2 accurately and reliably measures the nitrite level in aquarium and pond water. Nitrogen-containing organic substances, caused by leftover food and fish waste, break down in the water in various stages, leading to harmful byproducts. A nitrite concentration of more than 0.3 mg per liter is harmful to your aquarium or pond fish over time and promotes algae growth. It offers good long-term stability and a high range. Suitable for freshwater and saltwater aquariums as well as ponds.