Do nitrite test kits expire? I have a tetratest nitrite kit that is a couple years old now. I decided to check my five crayfish tanks for the hell of it and they all had low nitrite readings. Which is weird because the tanks are very understocked, overfiltered, and get weekly water changes. I have never had issues with these tanks before. Then I tested my other tanks that held fish at different stocking densities and got the same results.
