I don't know the volume of the Open Ocean tank where the mantas are kept actually and I couldn't see the answer with a quick google. It is a very large tank though and doesn't feel small even with animals the size of mantas. (they hold the smaller Reef Mantas of course rather than Ocean Mantas)
However the total volume of the whole place is 42.8 million litres (according to Wikipedia the second largest in the world) and the mantas are in the largest tank. I think that volume includes the dolphin tank too though which functions as a separate attraction with just some small viewing windows from the SEA Aquarium.
Wow! A huge animal up close. I have seen Manta rays at Georgia before but they were hanging out in the back. And their was bratty kids blocking my view.
