Aquariums: Can anyone help me identify this tank and its filtration system?

Hey! I randomly met a really sweet guy at the Salvation Army store where I was looking for a small glass tank nano tank, we struck up a conversation.. and he offered to give me his old tank for free as he was moving and lived across the street. Looks like he grew up with saltwater tanks in his family but decided not to keep fish anymore. Anyway, I’m less than a year into this hobby, and I have one successful planted community tank I matured and now is going strong with inhabitants. I’m looking to have a tank for a single Betta as well so this was a godsend. Anyway, I think he took off the filtration system before he gave it to me when I said I was trying to do a Walsted method? I have no idea how to find a way to replace the filtration part in this tank or how it works. Seems like an internal filter I got is too big/clunky for it and then I have to also put a heater. I don’t think there is anyway to put a hang in filter? Help me please?