Welcome!
From the picture you have an African Clawed frog. They are a great frog to have!

Lots of changes it sounds like and these frogs can be great sulkers when changes happen.

Luckily, they can go weeks with out eating and suffer no ill effects.

You are definitely on the right path - you bought a larger tank, you are filtering it, you are adding decholorinator to the water...

How large is the tank? Please make sure you have a secure lid, they are known jumpers.
What type of pellet are you feeding?
What type of dechlorinator are you using when you change the water?