I looked into this a few years ago. They list the requirements on their website.
Volunteer at the Zoo
I know you must own your own gear and volunteer a few times monthly. Used to require Rescue Certification and commit to weekday dives.
From the Website:
"Divers must be at least 18 years old, hold an open water SCUBA certification from a recognized agency (PADI, NAUI, etc.)."
"Scheduling varies, but divers must participate at least once per month and attend regular volunteer dive meetings to stay active in the program."
I know they have dives on weekdays and weekends.