Fish Lost Scales

[Beverly]

One of my fish, a 3" yellow tailed angel, in QT was thrashing around last night and this morning trying to get out of its tank. I must have been doing extra stuff on the kitchen counter where the tank is and the fish freaked

Anyway, poor guy/gal lost 2-3 scales in the process. Other than keeping nitrate low and ammonia/nitrite at 0 ppm (which it's been for weeks now), is there anything I can do to keep the fish from coming down with a bacterial infection? How long should it take for the scales to grow back?