Jim is right, Joists and studs are 16" on center.
and why would you even want to risk it?
I mean, seriously.
Is it not cheaper to simpy run new hooks into joists, then end up loosing an expensive light set up, loosing every last living thing in your tank, and possibly loose your tank to [ by breaking it ] ?
I sure as heck would go buy new hooks and find joists, then risk loosing thousands of dollars.
Your wife has a right to be concerned.
30gal; Bala Shark, Pl*co