Need help for discus

Hi everyone I need some help my uncles daughter passed away just 7 months ago and he wants to give me his daughters year old aquarium. It looks brand new and I'd love to have it but I was wondering if someone could tell me how much gallons it is. It's 8 feet long soo any ideas of how many gallons that is. I'm planning on pitting discus in there will they do good I've never had a tank that big. How many could I put in there

here's a tanks calculator

http://www.firsttankguide.net/calculator.php

an 8 foot tank can be many different sizes...... 6 is the best number of discus to have together.
Figure out what the tank holds and we can help you better.

probably a 210gal