I want to know exactly (or around) how much gallon this tank dimension holds....The guy who is selling it said it to be 180gal tank...I checked the calculator on here and it says 100 gal. but i checked on another website (http://alysta.com/books/fishtank.htm) and it seems to be around 120gal-130gal tank....can someone who knows there math and tank dimensions tell me...im confuse...TIA