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On Wednesday night Husbandry Staff participated in Salt Mix. For those of you not familiar with Salt Mix, after the aquarium closes, the Husbandry staff assembles after hours to pour salts into two designated vaults. The vaults are large cement tanks under the first floor gallery area. The day before Salt Mix the vaults are pre-filled with filtered city water (fresh water.) Each Salt Mix makes 185,000 gallons of salt water at normal seawater salinity (30 parts per thousand.) This will last Aquarium staff about 4 – 5 months.
Six major elements are added to the vaults in bulk; sodium chloride, magnesium chloride, magnesium sulfate, calcium chloride, potassium chloride, and sodium bicarbonate. Trace elements such as strontium chloride, sodium phosphate, lithium chloride, sodium molybdate, rubidium chloride, and cobalt sulfate are also added. Chemical elements added are mostly (66%) Sodium Chloride (NaCl) by weight. The total dry weight of elements added is 64,900 lbs. The new mix takes a week to dissolve, then is available for use in exhibits. During this time Husbandry staff must rely on large bins of saltwater that were filled prior to the mix. Any major water changes or tank maintenance is on hold until the water is ready.
Some interesting Salt Mix facts: The salt is ordered a minimum of thirty days before Salt Mix. We add .00034 grams of cobalt sulfate per gallon of water. One of the more expensive elements we add costs about $6 per gram. Normally there are two people dumping bags of salt into the vaults. Each “dumper” lifts approximately 16,250 lbs of salt per mix. In addition to the “dumpers” there are two “cutters” opening bags of salt. Each “cutter” will open 648 bags. Each bag of salt is individually counted twice before the mix begins and once after they are emptied.
Last night, it took us one and a half hours to complete Salt Mix. That is a rate of about 7.2 bags being dumped per minute or 180 lbs per minute. By the time the trucks are unloaded, the salt is staged and then transferred to the vaults, the forklift drivers spend about 9 hours total on the forklift on Salt Mix day. We estimate this is about 4 miles.
The saltwater we make costs about $9 per gallon. If we used pre mixed salt like Marine Mix it would cost about $15 per gallon. Adding salts in the wrong order can cause the salt in the vaults to heat up and solidify into an insoluble block. The 6 trace elements are added individually to the vaults. If they are mixed first and then added they turn the water purple. Salt Mix is a facility wide event; it involves all departments on some level. Special Events needs to ensure us that nothing is going on that night. Engineering will monitor the pumps overnight while the vaults mix. Security mans the main entrance to the Aquarium so that we can drive the forklift through after hours. Electrical is kind enough to put the house lights on in the Gulf of Mexico area. Maintenance makes sure the fork lift is in full working order, and Facility Services helps us clean up any salt that is left behind.
While Salt Mix appears to be a Husbandry only event, we really could not do it without the support of the entire facility.
I have posted additional Salt Mix pictures on Audubon's Flickr website.