API Nitrite Freshwater And Saltwater Aquarium Test Kit

Nitrite is the second spike of the nitrogen cycle — it appears as the filter starts converting ammonia, and it should fall back to zero once the bacteria colony matures, usually somewhere between four and six weeks. API's own note on why it matters is worth repeating: low levels suppress the immune system, high levels suffocate fish. This kit reads 0 to 5 ppm in both fresh and salt water.

What is in the kit

• 1 nitrite reagent bottle
• 1 capped test tube
• Colour card and instruction manual

When to test

Every second day while a tank is cycling, then weekly once nitrite has held at zero for a fortnight.

Looking after the kit

Rinse each tube with tap water straight after use — dried reagent stains the tube and throws out the next reading. Never wash tubes with detergent; the residue is harmful if it goes back into the tank. Shake the reagent bottles firmly, but invert the capped tube gently.

Pairs with the ammonia kit and nitrate kit, or buy all five in the Freshwater Master Test Kit.

API Nitrite NO2 Test Kit on the API website