Everyone's going to think that I have a knack for things going wrong in my tanks (I think this is my 15th post in the Emergencies thread), but here goes anyway. I would rather admit to a problem and get it fixed rather than pretend I know exactly what I am doing.
I had two twin-tailed goldfish in a 5.5 gallon tank. Moved them to a larger tank and put three guppy fry into the 5.5 The tank has been established for months now, and goldfish are notorious for producing ammonia, so I would have thought that three tiny fry would have been a piece of cake for the filer to handle.
All went well for 48 hours until this morning - one fry was dead, and the nitrite was at 10ppm with the nitrate at 20ppm. I have never had such a high reading in any tank, even during the cycling process! What went wrong? I vacuumed out the gravel and did a water change and am planning to do water changes until I get the levels corrected.
I think I overfed them; I crushed up a few tropical flakes for them twice a day, but when I vacuumed this morning there was quite a bit of debris at the bottom. It was hard to see what they ate and what they didn't since the flakes were powderized. Could that have caused such a huge spike? Or could the biological filter have died since there was such a drastic change between two fancy-tailed goldfish and three itty bitty guppies?