Hanna Instruments HI-98129 Combo pH/EC/TDS/Temperature Tester 

Model HI 98129: pH/EC/TDS/Temperature tester by Hanna Instruments has a completely waterproof shell that also floats. It offers high accuracy readings with dual-level LCD readout. 

This durable tester gives you a replaceable pH electrode cartridge and cloth renewable junction. The Hanna Instruments Combo provides both adjustable ß and TDS ratio. The stainless steel encapsulated temperature sensor facilitates faster, more accurate temperature measurement and compensation.

Battery level indicator is standard - battery life is about 100 hours of contiuous use, plus it gives you an auto-off function after 8 minute of non-use.

The Hanna Instruments HI 98129 has an EC/TDS graphite electrode that helps prevent contamination by nutrient salts!

Specifications:

pH range - 0.00 to 14.00 pH
EC range - 0 to 3999 µS/cm
TDS range - 0 to 2000 ppm
Temperature range - 0.0 to 60.0°C / 32 to 140.0°F
pH accuracy - pH ±0.05 pH
EC/TDS accuracy - ±2% F.S.
Temperature accuracy - ±0.5°C / ±1°F
TDS Conversion Factor - adjustable from 0.45 to 1.00
pH Electrode - HI 73127 (replaceable - included)
Battery Type / Life 4 x 1.5V / approx. 100 hours of continuous use
Dimensions: 6.4" x 1.6" x 1.0"

The Hanna Combo Tester has a stability indicator and automatic calibration. This durable piece of equipment weighs only 3 ounces.

Read Instruction Manual (PDF format - Lots of detail.)