Not sure what to do. I have 5 total plants, strawberry cough in coco and perlite. Using canna A&B at 6.2. Adding cal/mag in at 2tbsp between about 6 gallons of water. Running a little over 20% run off. TPS on run off is about 1490. The others look good. This one just won’t get right.
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Other may need more info to help but I usually ran cal mag at max 5ml/gal. Later in flower I ran around 2.5 ml/gal.
I also ph’d canna Vega & Flores around 6.5. I think they are suggesting 6.2 for their coco or coco/dirt mix but assuming you’re in dirt, calcium is barely picked up at 6.25 pH. Around 6.5 is in the prime to grab all nutes in soil grows.
My bad, you said you were in coco, guess that’s about on point but I don’t grow in coco so others can help on that
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I’m no good at diagnosing issues I’ve not experienced first-hand, but felt compelled to reply since I’m also growing in coco/perlite using the Canna line.
I know they recommend a ph of 6.2 when using their coco, but I aim for 5.8 as I’m using generic coco. I stop the calmag at around week 6 of flower and use Epsom salts until the rest of the grow.
Do you have the other Canna nutrients recommended for flowering? (Boost, cannazym, Canna PK).
Sorry I can’t be of more help; hopefully a more experienced grower will jump in. Or tag someone, like @Hellraiser
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I agree with @Sativafan up the calmag after flush and add some 1 tsp of Epson salt per gal.
Another thing you really need to consider is defoliation of your plants. It will probably help with a lot of the issues.
Also make sure PH meter is calibrated.
How high is your light?
Looks like you might have had some serious light burn.
Good luck! 
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I have the same symptoms just not as severe. I am hearing phosphorous def. I am trying to get Ph right (runoff reads low ph) to be sure but am also upping the TB .
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Had some Blue Dream autos that had the same look late in flower. At the time I thought light burn but now suspect Ph fluctuation and lockout of the phosphorous.
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That was going to be my post. N and P def it looks like. 1,500 ppm would be at the point I’d do water only until salt level drops below 1,200 ppm (in coco). That one plant is just being more sensitive to it than the others (different pheno). Add to that as the plant matures it’s experiencing senescence and older leaves will die and fall off.
Cal mag is always a good idea under high intensity indoor lighting.
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Thanks for the replies. My lights are roughly 20 inches above. 3 200 watt leds. The others look pretty good. Maybe that particular plant has a lock out? I’ve run a lot of water through it with half nutes because over heard not to run just water through. With the epsom salt do I dissolve it in the water or sprinkle it in the soil?
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Speaking of defoliating. I was always told
Not to clip anything once in flower. Is clipping leaves ok? @HappyHydroGrower
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Nah not nitrogen pure phosphorous deficiency from developing buds I have a decent amount in my organic grow every strain gets it slightly but it’s usually reddish brown spots that start at the tip and works it’s way down sometimes with yellowing and you can do light exfoliating during flower
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I think I would adhere to what @Myfriendis410 has stated. After all, he did teach me everything I know, 
Never get tired of thanking them!!
Water and get nutes where you want them and work on PH is probably the best thing you can do for your plant. If you ever do mix Epson salt, just mix it in water and then PH.
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Don’t chase runoff ph in coco. You’ll go crazy trying. As long as what’s going in is ph’d correctly and you water to runoff each time you’ll be good. How often are you fertigating?
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Most defol 21 days into flower and then again at 42 days of flower.
I stripped every leaf that protruded from the stalk at 21 days.
23 days after flip
Shortly after defol
And this past Saturday 7 1/2 weeks
I don’t know that it hurt or ever slowed them down. It helps tremendously with temps and humidity.
Good luck!
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I water every other day
I switched to 12/12 on March 25th
Ideally in coco you should be watering with nutes at least once a day . Take a read through this article.
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