My comet and fantail are in a 180 litre tank, they're a stunted three year old pair of fish that I rescued back in May. Anyway, something interesting has happened in their tank. The cycle is complete, I have a Seachem ammonia alert, shows clear. My test kit is showing clear for nitrite BUT also clear for nitrate too! I have two plants in the tank but nothing major. The tank has no running filter, only two cycled pond pumps (long story but yes they're cycled). There is a filter that is built in to the tank (Juwel 180) but there is no media, it's off and basically redundant.
So, how have I managed it? I do a small daily water change but I mean small, not enough to remove all the nitrate. I've heard of denitrifying bacteria, but I didn't think it existed in freshwater. I know it lives in water with a low flow rate so could it be housed in the dead spot of the switched off filter?
I did consider the Prime could be causing a false reading but all my other tanks are testing normally for nitrate. It's only my 180 litre that is totally clear for nitrate. It's been like this for a week now.