We send our DS-5X and MS-5 to the bottom of the largest acid pit lake in the world twice a year. The Berkley Pit (Butte, MT) is a former open pit copper mine. It contains over 43.7 billion gallons of acidic (pH~2.6), metal-laden water that is about 1,000 feet deep. We use our sondes to obtain pH, Eh, temperature, turbidity, and specific conductance profiles. Parameters from the upper 600 ft are collected using a direct-read cable; parameters below 600 ft are collected by lowering the DS-5X on a nylon rope and utilizing the internal data-logger memory. The profiles are used to monitor changes in water chemistry as the pit fills and as solution mining removes copper. The copper concentration is so high that it precipitates on metal iron surfaces, including the DS-5X bracket. Past uses have included deployment at multiple depths in the pit for up to four weeks of unattended monitoring. We put our sondes to the test under some of the toughest conditions around and they get the job done.