pH stand for the "power of hydrogen" and is a logarithmic scale for how acidic or basic water is. Low numbers are acidic, high numbers basic.
pH of Water - Environmental Measurement Systems
A system for monitoring water quality in a large aquatic area using wireless sensor network technology, Sustainable Environment Research
Examining the dynamics of the relationship between water pH and other water quality parameters in ground and surface water systems
YSI Water Quality Sampling and Monitoring Meters and Instruments for dissolved oxygen, pH, turbidity
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Quality of pH Measurements in the NODC Data Archives
pH of water (Environmental Engineering)
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Seagrass, a sustainable solution to ocean acidification
pH of Water - Environmental Measurement Systems
Hanna Instruments Singapore
pH Measurement, What does pH Measure?