Metal Corrosion in Water?

chemistry of the environment (even tap water), any electron flow through the probe to the sink (water) (in your case half of your cycle), and/or cyclic mechanical fatigue, will cause corrosion. the correct polarity DC charge is the only electronic way to fight corrosion. Frequency wont make a difference. Water is usually a good ground. More bubble on one of the probes is inconclusive. Also, stainless steel is still susceptible to corrosion. I would put an aluminum or magnesium anode on the probe.