Hi jimmy L here. I'm working at a resort that just open a new in ground pool and SPA. The Spa is roughly 1400 gallons. The ORP is set
for 710Mv and there is no problem with that setting as long as the jets are not running. When the jets are turned on the ORP starts to drop. Sending too much Chlorine. If people keep turning the jets on over & over again the Free Chlorine level will go from roughly 3.5/3.9 to 6.9/7.3 It almost seems as though the oxygen mixed in from the Jets confuses the sensor. even though you cannot see any air though the site glass with the sensor.