321-75 Ammonia ION Selective Electrode (BNC)ION selective electrode for fish tanks, biological samples etc About Ammonia Combination ION Selective Electrode. This electrode can be used with any convenctional hand held or laboratory pH meter with a millivolt mode. The sensor is fitted with a 1 metre cable, terminated with a BNC connector. No reference electrode or filling solution needed. Available in fully submersible and water proof format. Solid state sensors. Ideal for novices. Very