PH: PH has been fluctuating a lot. The pattern I see is that it is around 6.2 or so when I change the water and it remains pretty consistent there for 3 days. It might rise a small amount for the 1st 2 days...Up to 6.3 or 6.4 but never higher. On the 4th, 5th and 6th day, the PH starts to drop considerably. Typically on day 4 it will be 5.9. Day 5 it will be 5.5. Today was the 1st time I've gone 6 days without changing the water and it was 5.1 this morning.
That first part sounds good, it's supposed to climb a little. The EC should drop a little. And the water level should drop too. That second part you describe, about the ph dropping, sounds like imbalance from over-fertilizing. The ratio you give is never the exact ratio the plant takes up and the larger the difference, the bigger the issue. For example, it possibly sucks out most of the N and K which leaves a high amount, relatively, of P. pH fluctuations are often a result of an imbalance between cation and anion, between positively charged and negatively charged ions that is. Every time an elements This is also why controlling PH with products like Ph down (P or N acid) and pH up (K) is not very effective once that imbalance is fact - it often only makes it worse (ie. drop or climb faster).
Too much of one element, i.e. imbalance, messes with the uptake of others, even if there's enough of it in the soup.
It's highly unlikely that 1.0 EC is not enough in NFT to a point that it causes deficiencies. Cannabis also doesn't start using more nutrients drastically during early flowering compared to the transition/stretch period where it still adds on a lot of mass ( leaves and branches and roots). The symptom in the first pic looks like a deficiency but it's unlikely from a too low EC. The edges on the leaves in the last couple of pics look burned.
I always burn the tips of some of my plants on my tubes at the end of the stretching period, when they stop vegetating and need less nutes, the EC stops dropping and PH starts dropping. Then I lower EC, and build up, and lower again near the end. 1.0 EC from start the finish should work for pretty much every strain though, given a some balanced soup to start with.
What is the NPK ratio of the nutrients you use? And what type of PH down do you use? (I suggest nitric acid, not phosphor).
When I need to add water I won't add plain water. I'll mix up another batch with nutes and ph down as if it was a complete rez change.
That first part is exactly what I would suggest, don't add just water but add water with nutrients. That's doable if you run slightly below that spot where the EC stays stable (which isn't a goal nor ideal by itself). This is why I don't put the nutes for one week in a rez at the start of the week, I add a little every 2 - 4 days. Last run on my tubes I refreshed the rez entirely twice during the entire cycle, the rest I just added water and nutes. So I suggest lowering the EC to a point that you notice it drop a minimal amount every day or two. If the pH drops too fast, just add water (lowering the EC, raising the Ph). By itself some pH fluctuation between 5.8 and 6.2 is good, between 5.6 and 6.5 still as long as the soup is balanced.
Also, are those pics with the light on, or another light? Can you take some with flash in the dark, tends to show their natural color better.
Is the smaller one with the healthy roots affected too? Does the water still smell fresh at the end?