Xisha islands and Dongsha islands in the Southern China sea is worth diving since it's not yet developed, only fishmen go there (i dunno how much damage the fishing has got to the sites, but some divers go there and said it's terrific, i have seen some photos too, it was georgers.)
I am not into any aquarium diving as i dun want any aquarium exists.
However, it's not easy to go to those sites even for Chinese, i really dunno if foreigners can go there or not.
Hongkong has some dive sites and viz is about 3~5M i heard, sometimes can be better.