Salt water chlorinator waveform

[e100]

This is the voltage trace that I see from a SCR controlled chlorinator set to about half on.

I was expecting the voltage to always return close to zero, but it never drops below about 3v even though the corresponding current trace returns to zero.
(different time scale and the 6.4mv line is the real 0v as the scope is out of cal)

When switched off the electrodes generate a DC offset of about 1.2v which presumably is the battery effect.
So what causes the additional 1.8v offset on top of the base 1.2v during normal operation?
A Google search didn't turn up much and I'm not a chemist.