Fifteen bonnethead sharks at the Indianapolis Zoo have died because of too much ozone in their tank.
Zoo officials say two emperor snappers in the tank survived and are expected to recover.
Zoo senior veterinarian Dr. Jeff Proudfoot says the tank's skimmer system was taken offline Monday morning for repairs, keeping water from passing through that part of the system. Without water, an ozone probe could not provide an accurate signal and a generator continued adding ozone to the tank.
Ozone is used to purify water. Officials say the zoo will review the system design and procedures for repairs to help prevent a similar accident in the future.
The bonnethead averages about 3.3 feet in length and is found in the western Atlantic and eastern Pacific oceans.