Nice.
You said you are getting 420vAC across the water. Did you measured the current? I guess you are using deionized water right?
I think that when the voltage reach the maximum you should try gating the electrodes as for the electron extraction circuit this way the electrical energy generated by the water should get back into the inductor for the resonance to happen violently. However it must be aways unipolar otherwise you have AC with a DC offset.
Did you noticed the Current reducing under resonance?
Did you tried a air core inductor, with a long wire?
I noticed that you are using the secondary of the MOT, it has a big resistance, not only by the ohmic but a very big reluctance of the core.
Maybe with a smaller transformer you get better results.
I say this cause i tried many times to resonate MOT's adding capacitors in parallel and with few turns of air core i got resonance much easier.
With a lower value of inductance it will allow you to have a higher frequency witch would let you to charge the water faster without the ohmic losses.
If you find the right configuration where you get the right ratio of current to voltage, your resonance will be the maximum.
I also have here a a setup that i reach 400 volts however as the electrodes are much bigger mean that i'm using more amps than you. Anyway i see no gas here even if is DC. My diodes get burn i don't know what is happening. The diodes despite being ultra fast 1200v 30 amps rating, get really really hot with less than 0,200ma flowing. I was using a water that with my configuration had 3000ohms about 1,7nf...
I think that 400v is enough to move the ions, the thing is that we need to be able to capture them and transform into gases generating electricity and thus resonance.
The steps are:
Charge the water thru the inductor
Discharge the water thru the inductor
Inductor in my view serves for having a reverse voltage to short on the water with the reversed ions. Like getting the positive of one battery and connect to the negative of the other battery and than short the other poles. This way the thing should as the ions will generate a voltage a little bit smaller but with a current much greater, you should be able to recycle this electricity to charge the water again.
The concept in my view is this.
I think that the SS wire is useful here as it would let the discharge to be very fast due to the L/R time constant. MAybe the discharge coil should be small but having a resistive wire to ensure it will discharge as fast as it can. The copper will have a maximum time constant while ss will be much higher.