I'm currently cycling a 30 gallon tank, and as ammonia had disappeared in the last few days - only nitrites and nitrates present - I reduced the tests and water changes to once every three days. After all, if ammonia's gone and nitrates are already at 10ppm then the cycle's nearly complete and there's no real danger left, so no need to worry about tests and changes every single day, right?
WRONG!!! The fish were definitely looking listless and hanging at the surface when I came home last night so I tested the params... and found to my horror the nitrites were at 5.0! In fact they were possibly higher since my kit only goes up 5.0 (groans with mortification). They'd obviously still been rising fast and I hadn't noticed because I hadn't tested in 3 days - I assumed it was safe not to. Stupid! Stupid! Took 8 buckets to bring the level down to 1.0, i.e. nearly a 100% water change. No wonder the poor fish were listless! (They're much better since the water change, btw).
That'll teach me to be complacent before the cycle's properly finished - I'll never do that again! Just thought I'd share this with you so no-one else has to make the same mistake.
