Three people were taken to hospital on Thursday evening after a chlorine leak at the Takapuna Aquatic Centre.
A similar incident occured at the centre last November. Two people were hospitalised in that incident.
This time, 50 members of the public and seven staff were ordered out of the centre. Seven were treated at the Takapuna fire station.
The three in hospital are under observation.
The leak was noticed at 5.50pm and an all clear was not given until three hours later.
North Shore Mayor Andrew Williams says the 30-year-old centre re-opened on Friday morning.