Thank you for your reply @Crowthorne !
Do you think the possibilities of the aquarium re-opening at some later date are good ?
I wouldn't like to say. I think it closed due to structural reasons, as the Palm House is very old and very much overdue a refurbishment. But, as the iconic glasshouse at Kew, closing it for such a long time has been a major consideration (for reference, I think the Temperate House was closed for 4 years).