Do fish pace?

I've had a new tank with 2 green chromis for 2 weeks. One of the chromis has taken to swimming complete circles around the tank over and over. It'll do this for hours so I'm wondering if this is normal behavior or an indication of a problem?

All the water parameters are great with Nitrates being a bit high at 40ppm.

 

They will.... especially if they are not absolutely comfortable.

Your fish may feel nervous with the high nitrates, or he might just like to pace. Hard to tell until your nitrates drop.

I have seen some very odd behaviors over the years. That is part of what I love about this hobby. The never ending surprises.

 

I used to have a yellow tang, I think he was slightly off his rocker. My blue hippo use to splash me when I was sitting on the couch. These fish do some weird stuff sometimes. Lol, yea pacing could be normal for him. But you still wanna get your nitrates down.