Oh and perhaps there is a clue in the slow dropping of my pH, it drops about one point every day cycle?
For instance, my light runs during the night, so I'll go to bed and wake up and the pH will go from 6.0 to 5.9......
The EC has not changed ever.
So my guess is since it isn’t your light being to close. It’s not enough food for your light. I can over 2 EC no problems with clones that just started to show roots out of the net pot. They grow too fast so I starve them a little.
Does it list the ingredients in your base nutes? NPK values.
Roots look ok, not great, but ok.
I highly doubt it's a K def, but nothing is out. Just weird it's only at the top.
Light burn will fuck them up for a while, like a sunburn. Hurts the first day a bit, then gets worse even out of the sun.
Anyhow, your EC not changing is one thing, your ph dropping is another.
First the NPK values if you have them, and ingredients if they are there (phosphoric acid, etc).
My clones anyway go light yellow on the tops when they take longer to root. Bottom stay green. Ca deficiency??That explains the EC. Still not following on the leaves though. Older growth is green. Just odd.