I finally cycled my tank about 2 weeks ago. Its a 55 gallon with 3 medium size goldfish. I use 2 Emperor 400 bio wheels. I got nitrites and ammonia down to a reading of 0. Last night, my nitrites were back up to .50 Why would this happen? I had a spike of nitrites before it completed cycling but I had then added Bio spira and after about 6 days it leveled off. I am doing regular water changes, once a week(about 30%) and I am not overfeeding the fish. Any thoughts?

are you cleaning your filter?

I just changed the carbon filters in the back of the Emperors too... last week.

Does your Emps have a bio wheel, some times with no bio wheel it can jump up a tad. This isn't anything to worry about, as long as it doesn't stay this way. I bet it will be back to 0 tomorrow. Sometimes just the littlest things can cause a change (gravel siphon, changing the media in the filter, over feeding, adding a fish).

yep, I have 4 bio wheels in fact on my two Emperor 400's. I just did my weekly 30% water change, so i'll check the water parameters again in the morning

How are they today hun ?

If you clean your filter to often it will not have enough bacteria to hold your cycle i found this out the hard way i kept crashing my tank by cleaning my sponges in tank water every water change.