Hach Company IQ ISFET General Purpose Probes Optional probes for use with IQ 150 or IQ 240 Meters. Use general purpose probe for general pH testing; requires no maintenance and can be stored dry. Micro probe requires only 2mm immersion to obtain a stable reading and is ideal when sample quantity is minimal. Piercing probe with handle is designed for meat testing and other semi-solids. Use micro probe with piercing tip for applications that require minimal evidence of piercing.