I would bet active betta plus adjustment. Some get timid and some pace for awhile. It could also be reflection adding to his activity. As always with new tanks, monitor parameters. Perhaps try putting a cover over the tank for part of the day. Do you have a good number of plants (silk or live).
My daughter and I both have very active bettas. Our last one did a lot of pacing like yours the first week and settled down but was always active.

 

Ok, thank you! I am going to buy him some live plants tomorrow; I haven’t had the time to do so yet but my previous betta loved his plants. I will continue checking parameters and maybe today limit human interaction because that’s when he mostly seems to start swimming a lot.

 

Hi, you could mix live and silk plants for him to help give him more of a feeling of safety 'til the live ones grow. How big is the tank? Do you have lights on?

 

I just bought both small and large live plants and he also has 2 decorations he can swim in. He has a tank light and his tank is 3.5 gallons.

 

Experiment with the tank light (if by chance he's more comfortable with it off?), and keep an eye on the temperature of the water, just in case.

 

Sounds good. I have a heater and a filter that worked well for my previous betta, so I’m not too worried about water temperature and quality.

 

honestly, my betta is always energetic. He always greets me at the glass, and he usually swims next to his 11 tetras.

 

Hi, just a note based on experience of having things go wrong, as long as you're testing the water parameters including ammonia, you can relax a bit regarding water condition. However, be really cautious about relying on mechanical means to do the job.

 

yes. My betta is 21 months old. He has always been energetic.

 

I have water testing strips that I have used and will continue to use. I think Joe is just an energetic betta. Thanks!

 

Be sure that you're testing for ammonia. The strips aren't the best anyway, and the one multi kit doesn't include a test for ammonia.

 

Ok