Possible sick plants? Yellowing/patchy lower leaves, but fine otherwise

Hi all, 
 
Thought I'd get try to get this sorted before it became a larger issue - have gone through Google and the search here, without finding anything similar enough to make a decision (though the Google-fu is weak in this one...).
 
My Filius Blue and, to a lesser degree, Early Jal's leaves are starting to go a concerning yellow on the bottom leaves - new growth is fine, but the larger ones are looking a bit ill.
 
The plants right next to them are doing fine (choc fatali's in the pic for reference for 'happy' plants - sitting where they always do. But the Filus', directly behind, esp. the right, aren't). One plant in particular, on the right and in the inset pic, is looking quite pale anywhere below the latest growth and has a little patchiness on the leaves - the other FB of the same size is just starting to turn.
 
They're under 15w red/blue LED panels (x2, in light coverage), watered when they are bone dry and are in a mix of jiffy pot (because that's what I started them in) and a free draining compost. They've not been watered in about 6 days and are not wilty in any way.
 
No wilting otherwise, pretty happy in general. No fan - working on it.
 
Please excuse the inset - my battery died on my proper camera so the phone had to come out. Also please excuse the big pic - figured it was better that you could see what I meant.
 
 
Any help would be very much appreciated!
 
 

     What are you feeding them?

Thanks gents, 
 
They've not been fed as I assumed the compost would cover it for these early stages of their lives. I was more worried about the compost being too rich, to be honest, as it's pretty good stuff.
 

birdfather said:

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Thanks for this, however if I go through the above on the key symptoms, there's no single match or even a clear combined match - I went through this exercise when Googling as I was avoiding frivolous reposting of the same questions - next time I  will ensure I state the full extent of research I've done.
 
The likeliest possibilities based on the image above:
 
N:
Upper leaves light = no
Lower leaves yellow = yes
Bottom leaves (Cots at this point) yellow and shrivelled = no (dark green and healthy still)
 
Mag: 
Lower leaves turn yellow from inwards = no, they are uniformly yellow
Veins remain green = no, they are the same light greenish yellow as the leaves
 
Potassium: 
Yellowing at tips and edges = no, uniform
However - 'especially in young leaves' stands out, and:
Dead or yellow patches or spots develop on leaves = a small amount, yes, on one of the leaves.
 
 
I'm thinking it's potassium, but I am not certain.
 
 
I've given the one that's most affected 2oz of a generic 8:3:8 blood and bone type tomato fertiliser at 1/3 strength - if it's anything in there that the plant needs, should I see the leaves darken and become healthier looking, or stay the way the are, with only new growth being OK? In what timeframe should I see the leaves bounce back?
 
Your help is very much appreciated.

What is the PH of your water?

SichuaneseFoodFan said:

What is the PH of your water?

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Untested, however no issues with other plants that are being watered with it. I should test it to ensure it's in acceptable levels. 
 
It's interesting that this has occurred when the cups are mostly dry, with only mild condensation occurring inside the cups where the soil is not touching the cup directly (which ensures I can see the water levels of the soils).
 
On chlorine, contaminants: Using filtered drinking water - though our main water supply is high in chlorine at times, it's not at the moment, and the water that I am using has no chlorine smell and sits for a while before use to ensure it's dissipated. 

Chlorine from tap water doesn't hurt plants.  I even add pool shock to my reservoir to keep things clean.

SichuaneseFoodFan said:

Chlorine from tap water doesn't hurt plants.  I even add pool shock to my reservoir to keep things clean.

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Cheers SFF - old hyrdo user here, actually and genuinely for legitimate food crops, so assumed there could be an effect. It can certainly be an issue, dependant on concentrations, so I've always preferred 2(HO).

Alright - so there's now slightly 'wonky' curled growth on some of the Santa Fe's I've got growing, in the new growth.
 
Seems to still be a combination of everything - buggered if I can tell what it is. 
 
No further ideas?
 
Also going to reduce lights from 24x7 to 18 hours - they've only been in 24x7 for a month, and this is usually said to be fine to 8 weeks, so have discounted that as the issue to date.

Quick update after being away from the forums for a while due to work taking all my time - 
 
Threw some weak (30% strength-ish) calmag and micro nutes at them, with some blood and bone mixed in - they perked up and were fine after that.
 
Thanks for the suggestions, all - no idea what the deficiency actually was in the end, and I suspect it was a few, but it's sorted none the less. 
 
Many thanks, 
 
Dave.

GiantSmasher said:

Quick update after being away from the forums for a while due to work taking all my time - 
 
Threw some weak (30% strength-ish) calmag and micro nutes at them, with some blood and bone mixed in - they perked up and were fine after that.
 
Thanks for the suggestions, all - no idea what the deficiency actually was in the end, and I suspect it was a few, but it's sorted none the less. 
 
Many thanks, 
 
Dave.

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