I've been going through a fish-less cycle since just after Christmas, and other than a snag I had with pH (discovered I have soft water; i.e., barely any buffers in the water) that was rectified, the cycle has been going as expected. For the last four days ammonia and nitrites were dropping to zero overnight after dosing the tank to 4ppm of ammonia. THIS guide recommends a 90% water change after consistent 0 ammonia/nitrite tests to rid the tank of nitrates, so I did that last night. I then (maintenance) dosed the tank with ammonia following the same guide (I think 1ppm if I recall correctly) knowing that it would be at least 24 hours before any fish were added. Came home from work tonight and tested the water. pH is fine. Ammonia is 0ppm. Nitrites are off the chart!
Any clue why this happened??? No other changes were made to the tank.
Any clue why this happened??? No other changes were made to the tank.