Nitrite Test Kits. Use to safely adjust your pond water pH. Rainfall, water run-off, fish excretion, dead vegetation, rocks and other foreign materials may cause pH changes. The pH level should be tested weekly. Easy-to-use liquid test solutions for nitrite essential when cycling a new aquarium or maintaining ideal water parameters Match the color of the test solution against color chart for accurate test results. Toxic nitrite is produced by nitrifying bacteria in the biological filter as it breaks down ammonia. This kit tests for harmful nitrite and measures levels from 0 to 5.0 ppm. 180 tests per kit.