Hi all,
Thanks for taking the time to reply. I will definitely sort out the tap water PH so that we can resolve at least one issue.
@Jamie
It's interesting you mention the light arrangement. It is true that I did not have sufficient light the first few days, causing some plants to stretch more than usual. Since then there are 3 120W cool daylight and one Philips Son T agro 400 W (better for flowering).
This is not enough, I know, but I am hoping that, once I remove the males, the remaining plants will receive sufficient light.
For the last few days the lights are on a 12/12 regime. No further yellowing observed and plants are being transplanted today.
Again, thanks for taking the time to help...
FD