Merman

I should have added that the DC used is unsmoothed rectified AC so every 120 ? times a sec the voltage (and current) is reduced to zero, not too different from normal AC.

Sorry but don't fully understand "overvoltage hump" or the need to "get concentrated". AC will generate chlorine at opposite plates consecutively but I imagine at some frequency your supposition will become true. I would like to know at approx what frequency that is.

I think somebody has already pointed out that more expensive units change the polarity in the cell every so often to prevent the build up of scale on the plates. If this is so why not use AC? is there something about the characteristics of the plates that prevents this, or is it due to the needs of monitoring circuits. My unit uses two IXYS mcc 44-12 io1B thyristors with all connections used, and if you care to study the data sheet you might see what I mean about monitoring, I don't know whether there are triacs available to provide same polarity monitoring outputs. Unfortunately it's high summer here so can't afford to disconnect it at the moment long enough for a good study of the circuit.