72x17x24=128 gallons, so glasscages gives you an extra 8 gallons, the dims he posted 72x18x24=135 gallons exactly. I used the calculator here on P-fury, it's on the information page under calculators. Calculatorhttp://www.glasscages.com/?sAction=ViewCat&lCatID=2Those dimensions come out to 135 gallons, not 120.
125 wide.....not saying your wrong but maybe you have a diff. chart your looking at maybe the chart i have is wrong
but dont tell him that....let him think its 120...you might be able to bring it down a little more