Dielectric water coolant formulation (20kW xenon short-arc)

Yeah, I know its not a CPU. But someone here might have specific expertise with dielectric coolants...

So I'm revitalizing a collection of 20kW liquid cooled xenon short-arc military searchlights from the 1960s (AN/TVS-3) for a city-wide art project in San Francisco.

These require dielectric coolant with conductance <50 µS/cm, as the coolant runs through both the cathode and anode in series, and the start pulse required to initiate the arc is 45kV (once initiated, operating is 45VDC 465A).

We have a formula that works (50% dionized H20, 50% ethylene glycol, with sodium tetraborate added to balance pH). However, this has issues: there is a substantial amount of corrosion to the aluminum heat exchangers, and precipitation is causing damage to the (irreplaceable and stupidly expensive) gear pumps. To combat this, we added coolant filters to the system, these clog frequently.

We're looking to identify good additives that don't ruin the dielectric properties, or a completely new coolant formulation, and preferably a supplier (20-50 gal quantities).

Ideas?