Oxygen is vital for all organisms in your aquarium or pond. Reliable and accurate, the Tetra Test O2 enables you to easily measure oxygen levels to ensure suitable conditions for your aquatic life. A low oxygen concentration can cause inhabitants to suffocate and become ill. Oxygen is also crucial for your aquarium's biological filtration, converting toxic ammonia and nitrite to nitrate. The kit includes an easy guide and comparison chart, providing approximately 30 tests.