Mysterious Plant problems ?

Could anyone tell me what is wrong with these two different plants?

They both receive 70*F day 50-55 night.
Humidity range 40-60.
Grown in canna coco.
Canna coco a+b nutrients 10ml per 5L twice a week, third watering plain PH corrected water.

Plants a whopping 2months old lol
Plants 15-17inch tall.

Strain : unknown ??

PH always kept 5.9 - 6.1

Plant A is getting 20/4 250w CFL
Plant B has just started 12 hour light cycle 400w HPS

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About 3 weeks ago they had twisted leaves due to a possible nutrient overdose.
This was corrected and they resumed good health for a week, then the week after they started looking sickly.

All the plants in the garden have slightly droopy lower leaves, nothing too bad though.

Plant A has nice dark green leaves whereas plant B has slightly lighter green leaves, perhaps due to HPS VS CFL .

Plant B leaves ends are curling slightly, consult following photos.
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Reason why they are so old is that the plan was to correct any nutrient difficiencies before flowering them.

....well, obviously your fertz are being locked out. What is your EC? One thing I noticed is that your temps are too low. I'd try to get temps up....espically night temps. Mj stops growth at 57F. The cold temps my be responsible for the deformed leaves, or a stop in growth. Try to run your lights at night while the temps are the coldest outdoors. Get a spot dehumidifier to run during the "sleep" period for your plants. The dehumidifier produces heat to keep the babbies warm. Good luck.

An EC meter is not available and the plants are not growing in hydroponics but coco coir hand fed.
Like i said, the medium is regularly flushed with plain (ph corrected ) water . The water is soft water so should not have a high EC to start with.

How do you recommend flushing? Simply water or a very dilute fert solution say 10% regular feeding ( 1ml per 5L compared to 10ml per 5l ) ?

Possible to correct night temps but its difficult trying to avoid creating a heat signiture - outside is snow where the plants are !

i say flush with straight water and stop feeding for a couple weeks .

the temp between lights on and off should be with in 15 degrees.Run lights at night when coolest.