As i understand it 7.5 is still in the area of acceptability for growing weed but i would definatly say 6.8 is best or a lot better.
As for the plant i would say it is getting a slight bit better, recap us on what you have done up to this point from when you first posted?
The tiny leaves growing on top or the newest leaves look quite promising but the plant still looks like it is sucking those bottom leaves dry. Tricky on what i would do if it was me, looks like it is stabalising a little. There are a lot of options depending on what you have done and wether it is near the point where it needs watering! Please get back to us as the more info we have at this point the better. This pic looks better than the first one, not by much but better.
I wish i could just name its problem, sure dose look striking but with the bottom leaves dying from the middle in it sure looks weird. So many variables, distilled water, sterilised soil. Don't panic at this point and do somthing rash like transplant it, it could still be a little small to transplant from that pot or maybe you should considor new soil possibilities. All in all i think if it goes ok this plant might just make it, although a little stunted at first, nothing you could't tidy up later. I think you got a challenge on your hands but think it could be fun.
Since I first posted and settled on micronutrient deficiency as the most likely cause, I have given one good feeding. Unfortunately I did not fully flush the soil with just water before feeding which in hindsight might have been smart. I just made up a roughly 25% strength batch of Miracle Grow 24-8-16 (see pic) and ran it through til the soil was fully soaked. Have tried not to do too much else...I dont want to make it worse by getting too hasty.
As I mentioned earlier I got the soil PH tester to rule out that as a possible cause, and I'm still not sure how to proceed with that information? I'm also moving back to tap water. My tap water is pretty good PH around 6.6, PPM<100. My distilled water actually PH's to 7.5, PPM around 0. Think its any coincidence that the soil also PH's to 7.5?
However, this whole problem did start while still using filtered tap water in the beginning so not sure what effect the water change will have.
I also thought my box could use some tweeking so I made some adjustments to my hood and fan set-up and added Mylar to the walls (to replace the foil I did have which I now know was a bad idea) In an effort to lower the temp and reduce any wasted light. My constant temp has now dropped to around 76-78.
I do have Lime, new potting soil, a few kinds of nutes...just not sure if and what I should be doing right now. Guess I'll just have to wait and see.
Thanks again for all the help.