I have two probes. They consist of a stainless steel cylinder inside another, one held by epoxy and one held by acrylic. I can measure a voltage difference between them. I have placed them in tap water and applied a 5V difference across them then disconnected the voltage. The problem is that they act as a battery and hold a charge and then slowly dissipate the charge. I can understand this happening if the two cylinders were made of different metals, but they are the same. Any help would be greatly appreciated.