This is a high quality double junction replacement pH electrode for the pH Sensor. The probe is fully submersible (exluding the bnc connector) and suitable for constant monitoring. pH probes should be replaced every 6-12 months. They should never be allowed to dry out. The saying is "If it dries it dies". When changing the reservoir care must be taken that the probe remains submerged. Particular in system such as flood and drain where the reservoir is emptied regularly. Constant exposure will lead to salt build up and decrease the life expectancy.