gift of death

What you could do is take it back to the LFS and exchange it for some other type of yellow fish or even just something that just has a little yellow in it and tell your relative that it grew up or the colors changed under different lights or something along those lines. When it comes to gift giving or marital infidelity, honesty is NEVER the best policy. Trust me.
 
I personally went with a 90, as the 75 just didn't look proportional to me. I managed to sell my tank for a decent price, plus some others, and we built a stand, as people here want 500+ for a crappy stand with a 90, and just buying a new tank was only 270 with an overflow.
Find a store and see them side by side on a stand, that's what put m e to getting a 90.
 
The tang will be perfectly happy in a 75 or 90. Some say the absolute minimum is a 55, but I'm sure the tang would prefer a tank that is 18" wide, as in your plan. ;)
 
I heard people use 45 gal, but if i am going to upgrade i might as well go for the 90 anyways.
 
Bigger tank are always fun, and easier to keep. Have fun with your tang these fish are really intreasting to watch and always have a ton of personallity.
 
AquariaCentral.com