I would use a 400 ISO speed film because light is absorbed by water very quickly. It can be bright as the dickens on the surface, but once underwater, you'll discover it's pretty dark.
I'm in a similar spot, planning a trip to Hawaii in August.
Athiril, why are you using the 85A filter? I'm an ignoramus on filters.
I usually get nice results from 400 speed print film like Portra VC in underwater conditions, although it's usually a swimming pool! Ektar would probably be good and the price is good, but may be a bit slow if you're not using flash.
Any 400 speed should be fine. In shallow water (say 10ft or less) 100 speed would be fine. I find that when I shoot underwater (mostly pools with my d******) I have to compensate for the blue cast of the water by adding a red filter on.
What Josh said, the 85A (converts the overly blue sensitive tungsten film to look normal with the blue-drenched light of daylight... wow that sounded weird..) is to reduce the blue cast of underwater photography.