It happens with such regulatory in Thai BL, I suspect that the acquarium is rather like a house near in my grandmother's neighborhood in Pasadena. Though it may have burnt down since, when I was growing up, the house was one of the places our family would walk past: someone was nearly always filming, usually scenes that were supposed to take place in New England (the house has that look) with fake snow on the ground.
In Thai live action BL, characters commonly visit the local acquarium as well as the seaside.
Interestingly, this trope has passed from "Hey, the acquarium let's us film on their premises!" to a standard date for BL characters. That is, the date has become a trope, much like amusement rides and haunted houses! In the Japanese BL series, Stay by My Side After the Rain, the characters visit an acquarium for their first date after they got reaqauinted.
There is something quite inviting about fish. And the set-up is perfect for action-while-talking. Sitting in a theater is too static. Dancing is too noisy. The aquarium is perfect!