At the Aquarium of the Pacific in Long Beach, you can volunteer to clean their aquariums, but you have to do other volunteer grunt work for at least a year before they let you set foot in the aquarium and you probably have to do that every weekend, which is not worth my time since I would rather be diving. If you miss a weekend, you have to start all over=(.
Now, it's been awhile since I worked there, but you make it sound much worse than I remember.
I became a volunteer diver right away, no grunt work as you put it. I got to pick the day and shift I worked, and I even changed it a few times based on work changes. Everyone I worked with was really cool, and I was diving in the tropical tank my first shift. Feeding Queensland groupers whole sardines. I loved that job.
I took time off frequently when life or work got in the way, and everyone was very understanding. After a year, I got the chance to do full face mask training, and then I got the chance to give presentations to customers while feeding the fish and floating in the tank.
In general, I learned more about marine life and diving while enjoying marine life that you'd be lucky to see on a dive in the real world. All around, a great job.
Unfortunately, unlike other aquariums, you do have to apply and volunteer to dive there. You can't pay for a one off dive (unless that's changed). The AOP is a good aquarium, though. Get a full tour and check out the topside and inner-workings of the place.
I have noticed more and more that aquariums offer these dives for money. I live in Thailand now, and the Bangkok aquarium has two options. You can "dive with the sharks" for around 175 USD or suit up in a surface supplied helmet and walk with them for around 100 USD. I think I'd actually like to try the second option. Diving is something we all get to do, but under water walking with lead boots and helmets is usually left for commercial workers.
Anyway,