HDE Digital Salt Water Aquarium pH Meter and Marine LCD Thermometer with TDS Water Quality ppm Meter Pen This digital pen style pH meter is an ideal instrument for testing and maintaining your aquarium Excellent meter, very accurate and durable. Measuring pH Range: 0.0 - 14.0 pH. Resolution: 0.1 pH Thermometer has easy to apply suction cup and easy to read LCD screen; Temperature readings to within 0.1 degree TDS meter measures total dissolved solids and temperature of any water; Measures 0-9990 parts per million **Note: Calibration fluid is needed, but not included with this product