IETG own a large fleet YSI EXO3 sondes. The EXO3 is a purpose-built sonde for monitoring major water quality parameters, including: pH, conductivity, temperature, turbidity, ammonia and dissolved oxygen.
YSI 6920 V2 Multi-Parameter Water Quality Sonde
The YSI 6920 V2 sonde is an economical water quality logging system, ideal for long-term in situ monitoring and profiling.