Almost 8,000kg of glass are being replaced at Sea Life Blackpool.
Thirteen sharks and more than 300 fish have been removed while the new glass is fitted.
It is the first time in 23 years the tank has been emptied.
More top news
Latest weather forecast for the NW
Rivals square up ahead of rematch in November
Former Superintendant Roger Marshall has told the inquests - The police resources were completely inadequate... We were overwhelmed."