Read this -- Frog Forum - Pacific Chorus Frog

And yes, it's necessary to dechlorinate regardless of where you found him.

They are not very arboreal but will climb, so a tall tank isn't totally necessary with them, you do still need something bigger than what you have. Around here, I can find a new 10gal tank for around $12. I would get a screen top for it. They do like to burrow, that's normal.