As it was a "sneak preview", photography and video filming were not allowed. In the first few hours, most guests sneakily took photos with smartphones. After a while everyone pretty much did the same thing and it seemed okay to pull out the big cameras. This is Singapore, and if just one person breaks a rule (that is poorly enforced, and there isn't a penalty at all) everyone else will just follow

After a while, it is very clear that some staff members were tired of walking up to guests and ask them to stop taking photos. At least they were very courteous about it.
Photography and video recording are allowed during normal operations of the Aquarium, as long as lighting and flash are not used.