I believe they call it the aquarium is because the rooms are out in the ocean. I will see if I can dig up some photos, I've never stayed there but walked by a million times.The Decameron Hotels are all inclusive. I stayed at the Decarmeron Maryland during my first visit to San Andres, but found many more interesting places to eat.
Especially the lady a few blocks behind downtown that cooks stuff (I think think how to spell the stuff) in a huge pot of boiling oil for breakfast. The Maryland's buffet breakfast was good food, but not local food.
The Maryland's price was right as the total was a hair over US$200 for 2 nights and airfare (from San Jose Costa Rica), though the arrival time very late at night wasn't convient.