Maintaining a Constant Environment

The Shark Reef attraction at the Mandalay Bay Resort Hotel in Las Vegas, Nevada's only American Zoo and Aquarium Association Accredited Animal Care Facility, contains more than 1,200 aquatic species including sharks, crocodiles, piranhas, rays, sea turtles, jelly fish, and other various freshwater and saltwater fish.

The aquarium also houses five of the 12 known existing golden saltwater crocodiles, one of the most endangered species in the world.

Maintaining the water environment for these special species is a great challenge for the life-support crew. The exhibit relies on various analytical measurements to ensure the best water quality.

More than 1.6 million gal of water is recycled hourly through the vast arrays of pipes and water treatment equipment.

Approximately 0.3 million gal is used for the freshwater exhibits while the rest of the water, 1.3 million gal, is saltwater. In addition, approximately 4,000 gal of freshwater is delivered to the exhibit daily. The recycled and incoming water can be treated consistently, but only with the use of reliable analytical equipment. Salinity, pH, ORP, flow and temperature are the measured parameters, and controlling them ensures water quality.

Variety of measurements

In the exhibits, flow measurements are made using Signet paddlewheel sensors at many measuring points to ensure that the correct amount of water flows in and out of the various displays.

Salinity levels of the saltwater are monitored using a conductivity sensor with a salinity meter. The salinity is maintained at 32 to 33 parts per thousand. The salinity measurement is made using the Signet Model 5900 ProPoint Salinity Monitor and a conductivity sensor.

The freshwater exhibits must maintain a pH level of around 7, while the salt water exhibits are at approximately 8.2. The pH value of the make-up water that is sent to the freshwater and saltwater generation units must be monitored and controlled before it enters the unit in order to control the amount of added treatment chemicals.

According to Jack Jewell, general curator at the Shark Reef at Mandalay Bay, "Low or declining pH and alkalinity levels can result in HCO3 imbalance in the animals on a long-term basis."

When the water is recycled from the fresh and salt water exhibits, ozone is injected for disinfection purposes. Using a Signet ORP sensor and instrument, the ORP of the water is measured to ensure enough ozone has been injected. Later down the line, ORP is measured again to ensure the ozone and its by-products, such as hypochlorous or hypobromous acid, have dissipated out of the water. Any ozone left in the line "is an extreme irritant to the sensitive gills of the fish," Jewell said.

The water environment in the system must be maintained within tight parameters; anything outside of these parameters will be detrimental to the life of the sharks, golden saltwater crocodiles, and other aquatic life in the exhibits' fresh and salt water systems

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