I recently went to Manila Ocean Park for the first time in my life, and find myself wanting to share some tips that might make your (and maybe my) future visits better.
1. Avoid going on weekends: I went on a Sunday and there were a lot of people, most notably bus loads of children on school trips. Aside from the general ugh factor of having so many noisy, sweating people in one place, the attractions operate on a ticketing system that's 80% manual. Go when it's a bit less hectic and if unavoidable, inquire if there are any groups scheduled, and if so, how many.
2. Inquire for show schedules: I didn't see any show schedules explicitly put up (I didn't get a pocket guide, if there were any). The website only had a general guide and wasn't really that helpful. Ask for when each show is and how long it will last so you can watch all the shows. Note that you have to get a written time to be allowed in for the light and water show (called the "Symphony Evening Show"). A hassle since you have to make a stop in the reservation room, but understandable given the small seating and large crowd.
3. Buy a ticket based on what you have time for: Manila Ocean Park has many packages, including encounters and extra attractions. Because I came in the early afternoon and had the Liquid lunch buffet, I didn't have time to see the "Trails to Antartica" and the "Birds of Prey" attraction ( :( penguins ). You can finish all the attractions in one day… as long as you don't start mid-afternoon.
4. Skip the Liquid Pool and Lounge Buffet and eat somewhere else: It's seriously the worst buffet I've ever tried. While I did like their pork steak and fried fish fingers, as a buffet, it was seriously lacking: one soup served in the tiny "sabaw" bowls used in supermarkets, 2 unappetising looking pasta dishes (spaghetti and pancit), 3 viands (including those described previously) and a vegetable side dish of peas,carrots and corn. The desert had local fruits, bad buko pandan and fruit salad.
5. Bring a camera or a phone equivalent: not just to take selfies but to record your experiences at the park. Aside from the attraction, the bay offers some nice sunsets. Also, please don't use flash photography when there are signs telling you not to (even in darkened exhibits, it seemed like there was still light from all the heedless clicking - not cool).
On a side note, the park is not wheelchair friendly.
The park is small, but it's actually an enjoyable place to visit. Hong Kong's Ocean Park is a lot bigger, but if you can't go to Hong Kong, this is pretty good, even without the Pandas.