Fish Acting Unusual

[Galaxygal21]

I recently put my Betta fish in his new 3.5 gallon tank. He's been acting different since then. His fins seemed clamped and he stays at the top of the tank mostly instead of swimming around like he was when I instantly put him in. The tank is cycled and was safe for him to go in. I don't understand why he's acting different and I was thinking it's because he's not just used to such a bigger tank. Should I have done something different or did I do something wrong?

 

[Colin_T]

do a 75% water change each day for a week and test the water quality. If there is a chemical in the water, the water changes will dilute it and should make him feel better.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Make sure the temperature is correct.

Make sure there are some plants for him.