I posted this over at the PCC yesterday. I was thinking it would be nice to have an updated and more extensive coral reef theme. Rather than just having the one type of coral, the staghorn coral, it would be great to see: brain coral, table coral, and maze coral. All could be designed so that fish, sharks, and seahorses can "perch" on them, just like the current coral. You could also add in other stationary scenery like sea fans, tube sponges, and anenomes. A giant clam would be cool, too.
And we need a lot more variety in fish, such as jellyfish, pufferfish, clown triggerfish, clownfish, needlefish, parrotfish, lionfish, barracudas, and gobys, as well as shrimp and smaller green sea turtles. Especially the jellyfish and pufferfish. I can't believe we don't have those.
Also, a school of small fish like anchovies, formed into a school all facing the same direction and attached by clear plastic or something would be neat. Perhaps smaller reef sharks, too. I think it could be a really beautiful theme, with so many pretty colors that would be eye-catching for children, and yet still realistic.
In fact, instead of adding a bunch of divers or mermaids to it, they could make it a big public aquarium, so that regular people could be visiting and looking at the pretty reefs and fish.