Thanks, weedhound. I can drop the pH a bit more. My run-off is always about the same as what I put in. No plans for nutes until I figure it out.

It really does look like a calcium deficiency from the photos I've seen of it but then it also looks a little bit like a magnesium deficiency too. :wtf:

The pots are about 2 gallons/7litre and 10"x10". I don't think they are root bound, they were re-potted a week ago. Plus I noticed from the last root-binding experience that they seem to get pretty droopy at night when they are running out of root room and they're not really doing that right now. (the re-potting "fixed" that) I was going to put them in larger pots when I put them to flower in a couple weeks. I am running out of room and have to do it soon. I never expected to have 5 plants. (I put in 4 seeds and this is what I got)

Bloody frustrating figuring out what these plants want. For a "weed" MJ sure is picky.