Apera Instruments SX625 Replacement Probe is the replacement probe for Aprea SX620 pH Pen Tester. This replacement pH probe is equipped with a slim 8mm pH electrode and a built-in temperature sensor. It has a measurement range of 0 to 14. 00 pH and 0 to 50°C(32-122°F). Its 10 mm diameter probe allows measurement in most test tubes, making it perfect for educational use as well as other general water solution's pH measurement, such as hydroponics, aquaculture, pool & spas, small volume sample like saliva and urine, water treatment, environmental monitoring, etc.