You might want to consider a lower-form of algae eater rather than a Tang, Danny. That's a big commitment - seriously... What about the snails/sea hare route?
And yeah, that big a change in lighting will often give what you have now. I took 2.5 weeks to ramp up when I got my MH, and it wasn't a problem for me. (Of course, you want to turn them on NOW, and get that full photoperiod you paid so much money for...
)