PH rises and PPM rises in DWC after Neut change out

Growing 4 plants in DWC with 25 gal R/O water in reservoir. Air temp 75 degrees water temp 67 degrees Humidity 41% in late bloom. Using AN Sensi Grow and the full line of AN neuts. I mixed A+B at 60%, the additives I mixed according to AN neut calculator. After mixing Sensi Bloom A+B my ph with r/o water was 5.6, PPM. With the 700 scale PPM was 1390. At 0800 hours next AM my PPM was 1710 and my PH was 6.0. I am using a BlueLab guardian monitor which is new and calibrated. I added R/O water to full line in Reservoir and PH came down to 5.9 and PPM dropped to 1570 after adding 7.5 liters of R/O water to bring down PPM and PH. I have a water chiller with a recirculating pump, no slime, roots are healthy. I have a large air pump with 7 air stones, one at each pot and 3 in the center of the res lots of O2 in system. Before adding new neutrent I ran a air stone in mix for about 30 min before adding to res so I must assume that my mixture was thoroughly mixed.

My question is: Is this normal for PH and PPM to fluctuate this much in 24 hours. Why did my PH and PPM fluctuate so dramatically? Is this fluctuation normal?

Mixing maybe? Takes time sometimes for it to disperse in solution temp change can fluctuate ph so if your r o water is one temp at start and then warms or reverse.