Nitrites question.

I thought I finally had all my tanks situated and where they were supposed to be BUT....
Tonight is test night and I discovered high nitrItes in Bert, the Betta's 5.5 gallon tank. They were between .5 and 1ppm. No ammonia and slightly less than 20 in the nitrAtes. I was so surprised I repeated the nitrIte test and it came up the same. I didn't know you could have nitrItes and not ammonia, OR that you could have nitrItes WITH nitrAtes.
I had done a "quick" cycle with Nutrafin Cycle along with used media in the filter before I got him two weeks ago. Last week's test was 0, 0 and 10 nitrAtes. I did take out his HOB filter and replace it with a sponge filter on Tuesday but ran the HOB AND the sponge until removing it on Saturday.
I replaced about 1 1/2 gallons of water tonight and added some Prime. He is fine, or looks and acts fine. I also have some floating plants in the tank.
Do I need to get nervous or it this part of cycling in a small tank, (with an impatient owner)? I am careful feeding him and he only gets 3 or 4 NL Spectrum pellets twice a day. He eats them all without fail. I do worry because I hear about all these poor Bettas that look and seem fine and suddenly are flat out on the bottom of the tank, gasping for air or have rotted tails. He looks great.

Everyone else tests at 0 ammonia, 0 nitrItes, and right at 20 nitrAtes except the two with more plants and they are about 10 NO3.

It's has just not completed cycling. It takes time to establish the cycling colonies (and the bacteria multiple at different rates), which is why you can see many different readings. I expect you just put it back a little bit when you swapped your filters over. Definitely a good thing to run that HOB while the sponge was there, but usually I find it takes a week or two to fully seed it (depending on the bioload, and how established the filter was that the seeding came from). Just keep doing large water changes, and your bacteria populations will catch up. No worries. I'd keep feeding to a minimum until you have finished it up.

Thanks, what I read said I had rushed the cycle and also they were difficult with small tanks, but I was hoping with the extra help from the used filter medium and obviously not a large bioload with one betta I would be okay. I will keep an eye on the tests and use the Prime to protect him... I understand it is effective for 48 hours.
He is obviously NOT being affected...he thinks he's a puppy and comes rushing over every time I sit at my desk. I expect to hear him barking soon!  

It has been my experience that with tanks below 10 gallons you tend to have fluctuations in the beginning. I am not sure if this is the norm, but this is how it has worked with us. Belle, our female betta, is in a 5.5 gallon tank, and it took a while for it to establish, despite moving over seeded media... the readings were never alarmingly high, just enough to notice and change the water out. Her tank, however, has been reading perfectly for the last 2 months, it took about 1 month to get straight healthy readings. Many water changes on our end. The same thing happened with our 6 gallon tank, home to Sonny, our male betta. For the last two weeks, his readings have been consistently good... But it fluctuated for the first bit. I don't recall the nitrites ever getting as high as what you are reading, but, I would just keep up with water changes and allow it to establish. Keep us updated.

Bert's nitrites have stayed down since the water change... only the slightest purple tint off of the blue color in the test. And, NitrAtes rose a bit so at least I know it is working correctly. Still no trace of ammonia, whew.
This morning I sat down with my coffee and turned on his tank light. He was sleeping on his betta leaf and I swear, he stretched all his fins and yawned before he swam over for his breakfast. I am still waiting for the barking, though!!!