The Fritz Nitrite Test Kit is a liquid reagent test for measuring nitrite (NO₂⁻) in freshwater and saltwater aquariums. Nitrite is the second toxic compound to spike during a tank's nitrogen cycle and is lethal to fish even at low concentrations — testing for it weekly (and daily while cycling) is essential. Pair with our other water testing kits and water care supplies. Why Test Nitrite Critical during cycling — nitrite spikes between the ammonia and nitrate phases of every new tank's cycle Toxic at low levels — even 0.25 ppm can stress and kill sensitive fish Diagnose a stalled cycle — persistent nitrite means your biological filter isn't fully established yet Should always read 0 ppm in a fully cycled, healthy tank Specifications Brand Fritz Aquatics Tests For Nitrite (NO₂⁻) Test Type Liquid reagent + color comparator Water Type Freshwater & saltwater Target Reading 0 ppm in a cycled tank Recommended Pairings Fritz Ammonia Test Strips Fritz GH Test Kit Browse all water testing kits Water care & maintenance FAQ My nitrite is reading above 0 — what now? Do an immediate water change (25–50%) and add a dechlorinator that detoxifies nitrite (like Fritz Complete). If you're still cycling, continue dosing ammonia and testing daily until both ammonia and nitrite read 0 and nitrate is showing. How often should I test? Daily during fishless or fish-in cycling. Weekly for established tanks. Anytime you spot fish flashing, gasping, or unusual behavior. Are liquid tests really more accurate than strips? Yes — significantly. Strips work for quick screens but liquid is what you want for diagnosing real problems.
