Thank you all for the information.
The pH may have been off, but I corrected to 5.6-5.8 range (prefer to keep it a little bit lower to compensate for added nutrients). I did not use Cal-Mag, however I ordered Hydroguard to assist.
The temperature of the water, unfortunately, is hard for me to control. The current temperature is 22 degrees Celsius. Any suggestions other than getting a crazy expensive water chiller (which isn’t for me)?
Minimal nutrient use (maybe a tablespoon the first week - this is day 9).
As for the Rapid Rooter, I considered that it might be a bit too wet, but moving the tube was difficult (because net pot holes were too small). However, a Girl Scout Cookie Auto and Bubba Kush Auto in the same DWC look healthy in the background (see photo)
Needless to say, I lost the Pineapple Express Auto - the roots did look okay, so perhaps it was the heavy watering on the Rapid Rooter (although the leaves were not curling down much).
Thank you again, very helpful.