i have a similar issue with the conductivity probe, jumping around by a significant amount. Yes, it may be the effects of micro bubbles, but if that is the case, why is my old P3 probe which is inches away not having the same issue, I got a replacement temperature probe because the old one was reading significantly higher than the P3 probe and a lab grade thermometer but i still have the same issue with the salinity probe. I've calibrated it a number of times now.(if you are wondering why i have both P3 and P4 in same tank it is because the P3 is connected to my old doser and Ive been waiting months now for a doser 2.1)