In the previous post on wreck diving at Usukan Bay... just wanted to make a comment (but thread has been locked).
Usukan wrecks are not really suitable for Nitrox as some parts of the wrecks are at 35 metres or more and if diving with 32% nitrox, maximum depth will only be about 32 metres thus the risks of O2 toxicity will be very real. It is better to dive with compressed air abeit a shorter dive.
I have dome multiple dives at Usukan and one of the best precaution one can take would be to hang tanks at 3-5 metres depth from the boat with a regulator to ensure that all divers have enough air to do a complete safe stop of if deco should occur, to adequately clear their deco.