Not an O3 user...so feel free to ignore my post...
Rather than invest in O3...perhaps just invest in more/better traditional filtration equipment. Ask the owners of GCs and RGCs if they use O3 on their pond systems. I think you will find there is a reason. Far safer techniques result in as good or better results. My pond is always over 300mV without O3, PP, or other oxidizers added.
You would dimension O3 gnereation anywhere from 0.5 to 1 gram for each 1000 grams in the pond. To get generate the O3 the size of the unit will vary depending on if you are feeding it only compressed dry air...or oxygen. If you do the cost of an O2 generator, the O3 generator can typically be half the size compared to one being feed only dry air. Then you need a mixing chamber, a venturi to suck in the O3 from the generator, and an ORP-based controller to turn on/off the O3 generator.
Clearwater Tech Corona Discharge Ozone Generators, CD, 2.8 g/hr w/air, 7.6 g/hr w/ oxygen, 7 scfh air inlet range, 2 amps, 18