Looking good man! The system is coming along nicely!
I did some digging on this. Most generally, ORP treatments seem to range from suggestions of 650-750 for treatments. I remember treating Ich with potassium permanganate and using ORP's in those ranges also. Here the pathogens, in general, are considered to be oxidized by the "potential" rather than the oxidative product used. (e.g. similar orp levels required for differing chemicals).
Heres a couple papers that cover dosages and contact times for various pathogens.
http://alphatechpet.com/documents/lotus pro/ATP lotus PROSummaryPathogen 2012b.pdf
Here's a chart that compares ORP level with Ozone PPMs at lower concentrations.
Here is another for higher ranges.
Last is a paper that was specifically looking at ozone in nutrient solutions. It also looks potential nutrient loss from ozone (Fe, Mn).
http://wwwlib.teiep.gr/images/stories/acta/Acta 691/691_46.pdf
It seems that sterilization (not control) of most things (including pythium) is recommended as 2ppm of Ozone. However, I can not find ozone dosages for the specific pythium that we deal with in root rot and hydro (since there are 130 types). Though the last paper did note control of pythium at 3.5 ppm (lowest tested).