Dear Snoopy
Welcom to Taiwan!!
I also live in Taiwan, and been to Green Island twice.
Green Island is famous by its clean water,
the viz is always over 20 even 50 meters.
Variety of coral and fish make Green Island's underwater world beautiful.
And due to close to Taiwan island, the cost of food is cheaper than Orchid Island located south from Green Island.
You could contact Water World to arrange your trip,
but just as jc928tw said, pay attention to the Typhoon report.
Cause Typhoon is on the way to Taiwan today.
If you are not go to Green Island,
the north east coast of Taiwa is another great option.
It's close to Taipei, and we do shore diving there almost every weekend.
It not so good as Green Island, viz is always around 5~10 meters.
But you could find some place have different beauty to Green Island.
Due to the current and make some point have beautiful coral.
And since we don't have time and money to go diving in Green Island every week,
Diving in North East Coast near Taipei make us can go diving and back to sweet home at night.
Hope you will enjoy your trip to Taiwan.
if you have any question don't hesitate to ask me.
Steponwind