it varies between fish of course, but it'll probably take around 2 years for a typical large angel to grow from a small size to 8-10". to get to the full adult size, the proper environment (aka big tank) and a few more years will be required. fish's growth is logarithmic; very fast in the beginning, but once it hits a certain size the growth slows down significantly. once the fish hits 10", it may take another 5 years to get to 14-15" full adult size.
please have a read on this article about large angels and its proper care requirements.
Part I:
http://www.advancedaquarist.com/2008/1/fish
Part II:
http://www.advancedaquarist.com/2008/3/fish
and also the tang sticky:
http://www.reefcentral.com/forums/sh....php?t=1946079
in general, large angels and tangs need bigger tanks than same-sized fish of other species, much because they are more susceptible to stress from cramped environments. a 10" koran angel is going to need a lot more space than a 10% trigger.
copper in the QT is a good choice. run the cupramine dosage at 0.35ppm instead of the full 0.5ppm, since angels and tangs are more sensitive to copper. take 3 days to ramp to that dosage (0.12ppm per day), and test the copper once a day to make sure the concentration does not change. closely monitor the fish; if any displays distress, lower the copper concentration right away. depending on the circumstance, it may be necessary to switch to hypo if the fish cannot take copper even at 0.35ppm. though, out of all the fish i've treated for, i only had one fish that was really sensitive to cupramine.