A simple setup I made to free me from watching the time and manually turning the PWM on and off during conditioning. Does not exactly follow documented on and off times but I am satisfied with it. You can adjust timing by playing with the values of C3, R1, R2, and R3. Make sure R3 value is less than half of the sum of R1 and R2 values. See national semi datasheet (50% duty cycle oscillator). As noted use only the cmos version of the timer 555.
Needs a PC ATX power supply to power the PWM. I used a 400 watts unit with its +12V output rated at 20 amperes. It is more than adequate for conditioning.
I still have to manually replace the mucky water though.
