Everyone don't get their panties in a bunch. I recommend to just take a breath and a step back before you speak to Tenecor. They are already making you a new tank and admited that it was their fault, and they are making it right for you.
Yes they built me a new tank and let me keep the old one. Originally they were going to have the defective one shipped back, but the difference for me is my location. I live in Hawaii, and after eating a 750g tank I didn't think they wanted to pay for shipping a tank that large back.
I just played it cool with the thought I may have to send it back OR maybe they may just let me keep it. They told me the same thing that they were going to expedite it.
Then when I recieved the new tank I asked them what was the plan with the old tank. I was then told I could keep it.