If you can tell me the missing aquariums, I'd like to add them to my spreadsheet.
You had asked not to include aquariums within zoos, but I didn't know whether you wanted to include marine parks. To me, any place that displays non-domestic animals is a zoo, so it's all what you're looking for. Some places, like Underwater World in the Mall of America don't have aquarium in the name, but are clearly aquariums. We could probably discuss Dallas World Aquarium all day. Clearly they've added a lot of non-aquatic animals, but they're still in one big building, so to me an aquarium. Of course, again, to me an aquarium is an aquatic zoo, so probably splitting hairs.
I haven't been to Steinhardt since they moved, but I don't remember it being up there in size with the bigger aquariums before the move. I would think definitely Tennessee Aquarium (Chattanooga) would be in the top 10 in number of species. Others that might be in the running I would say would include Denver, Newport, and Camden.