5N AT AQUARIUM?

last yr at the mandelay bay [vegas] aquarium i had my 5n /kit combo. the kit lens was too slow and not many keepers for me. i'm going again with my 5N & 50 mm 1.8 sony lens. i'd like to hear some setting you guys would start with. i'm thinking S mode at 200 - meter mode spot - white bal in auto. i'd greatly appreciate any settings. the aquarium is dark & large with fish big & small swimming over head and all around. thanks