Calcium def?

I think you're spot on thinking its a cal-mag issue...
Hopefully the lime will balance everything out.
Good Luck.

 

Interveinal chlorisis and necrosis is not a calcium issue. This is probably a magnesium issue but I have never seen it present in quite this manner.

How much Epsom salt did you use. Plants cannot heal themselves so what is dead is dead, and sometimes it can take a few days before the damage can be stopped.

A complete picture of the plant, the temperature, the humidity, the solution pH, EC, and the volumes of what products you use per gallon are all necessary before the problem can be identified.

 

A tablespoon of Epsom salt?!?!?!?!?!

You don't know what you are doing but I can help.
1 tablespoon is 15 grams.
15 grams is 15,000 milligrams.
15,000 milligrams of 9.8% magnesium is 1,470mg of magnesium.
1,470mg in 3.78 liters is 388.9 milligrams per Liter, aka "Parts Per Million"

The normal ppm for magnesium is between 20ppm and 60ppm. While you didn't want to tell me how many ml/gal of the Coco A+B I can assume your value is somewhere in the low end of this range. Adding nearly 2,000% more magnesium, plus the lime, is going to absolutely ruin your grow. Do not use 1 tablespoon per gallon.

I don't know who told you to use that much Epsom Salt but you should share their name with us so we know who not to trust. 1/8th of a teaspoon to 1/4 of a teaspoon of Epsom Salt per gallon of water is plenty if it is even required.

I also notice you didn't list any of Canna's products designed for use in flowering. Cannazym at 0-2-1 and PK13/14 at 0-10-11 make a huge impact on their program for flowering and are more or less non-negotiable to get the proper NPK ratio required by the plants. In addition to this your grow room environment needs work.

The temperature swings too much. 72f to 78f would be a HUGE improvement over the current temps. As well, increasing the humidity to more like 45%-60% would help the plant control its metabolism a little better, and help with the burning.

6ml of A and B, 8ml of Cannazym, 2ml of PK13/14, and 1/4tsp of Epsom Salt would be my chosen solution if this were my garden. I would aim for a 1.4EC and would consider a foliar spray of 1/8th teaspoon of Epsom salt and 1/2tap of Fulvic acid in 1L of water. Additionally, pH down products made with Phosphoric acid are especially problematic for coco growers. If you have a pH down made with phosphoric acid I would suggest switching to one made from Nitric Acid, or organic acids like Fulvic or Citric (hydroponic stores or online). Coco has a propensity to retain phosphorus and an excessive amount of pH balancing could be a source of your concern.

You should really take a look around the coco forum. None of the seasoned growers I know of uses Lime in coco anymore because takes too long to break down in hydro and it skews the pH. Even organic growers are starting to distance themselves from lime, preferring sources like gypsum, oyster shell, Azomite, and rock dust for micro elements. Just keep learning and keep good records to improve every grow from the last.

 

A teaspoon of Epsom Salt:

5000mg x 0.098 = 490mg of Magnesium
490mg / 3.78L = 130ppm of Magnesium

So your solution here is to use twice as much magnesium as could possibly be necessary? This will definitely upset the chemistry, namely the uptake of competing cations like potassium and calcium, and possibly locking up Phosphorus in a precipitate. Let us also not forget about the 150ppm+ of Sulphate added to the mixture and how that will impact the uptake of other elements. In short, it's a bad idea and I don't care who recommended it.

The reason volume is important is because you can do the same calculation with the percentages on the bottles. I know that Canna A+B contains 1.2% Magnesium. So... if you used 6ml of that then...

(6000mg x 0.012) /3.78 = 19ppm of Magnesium minimum

If you were using twice as much, 12ml, then you'd have twice as much minimum magnesium. But I cannot know how much you have if I don't know how much you used. It also take far more effort to defend keeping your volumes a mystery rather than to simply say "I used Xml per gallon..." I dunno man... I dunno... What I do know is that going from 20 to 30ppm of an element to 150-160ppm of that element over night will only cause more problems than it solves.

AskEd himself, the local coco guru, stopped using Lime months ago and does not recommend other people to do so. He cannot update the first page of his coco guide, but nonetheless, he's not doing it. There are very few who are... as lime depends on a organic process to break down and as a hydroponic media there isn't a lot of organic action occurring. Lime added at the very beginning of the grow might be somewhat available towards the end but it just takes too long to become available. With all the runoff we depend on in coco, most of what is added and even made available is washed out and replaced with the dependable nutrients.

You came here looking for help and I provided to you an exact formula for your problem. I am very familiar with Magnesium deficiency and have resolved it many times in coco. I am also very familiar with Magnesium toxicity... You can choose to follow your own path and learn these same lessons for yourself or you can choose to listen to my advice and benefit from my experience in this matter. It's up to you and either way makes little difference to me.

I do wish you the best of luck and I hope you stick with the coco. It's great stuff once it's dialed.

 

Yeah, I was going by the gallon.
I don't think you need to flush, but you probably don't need more Epsom for the next 2-3 feedings. If you're willing to try it here's some feeding suggestions.

Wednesday:
4ml of A&B and 6ml of Cannazym per gallon to get at least 1liter of runoff per gallon of media.

Use 1/8tsp of Epsom salt in 500ml of clean water in a spray bottle. If you have either CannaBoost or Rhizotonic you can add 1/2tsp of one of these as well. Otherwise a small drop unscented biodegradable dish soap like Ivory or Dawn will work as a surfactant for the foliar spray. Apply this mixture to the underside of the leafs just as the lights come on. If you don't have a spray bottle, or unscented biodegradable dish soap, then head to the store, it will set you back maybe $4.

Thursday:
Apply another foliar spray. Make it fresh and direct the spray under the leafs.

Friday:
6ml of A&B, 8ml of Cannazym, 2ml of PK13/14 per gallon to get 500-600ml of runoff per gallon of coco.

Saturday:
Foliar spray but with just fresh clean water, nothing added. Feel free to really wash them down. This will clean the stomata of residual salt from the previous spraying. This is the last foliar required and you want to be very careful about the buds and the humidity. The sulfur in the Epsom spray offers a defense against mold spores but this rinsing during flowering does carry some risk. Do what you can to crank up the fans and keep the humidity under 60% (40% after this would be perfect, but that's tough).

Sunday:
3ml A&B, 4ml Cannazym, 1ml PK13/14, 1/4tsp Epsom Salt per gallon to get 1 liter of runoff per gallon of coco.

Going forward:
6ml of A&B, 8-12ml of Cannazym (increasing as flowering progresses), 2ml of PK13/14 until 20 days before harvest. 20 days before harvest cut the PK13/14 out, increase the Cannazym, and consider dropping the A&B to 4ml. 10 days before harvest drop everything and just use water, collecting a normal amount of runoff every day to starve the plant of additional nutrition and to make her consume what she has to produce that last burst of ripening energy. If the magnesium issue seems to be coming back then work in "Sundays" half strength feed with a little extra runoff between normal feedings. Temperature is a huge factor as well, so I want you to keep them temp under 78 degrees and if it goes over 78 and you see new damage to the plant then you know that throwing more salt on her isn't the solution to your problem. The problem is a strain that needs cooler temperatures to regulate her metabolism and you either have to give her a cooler environment, add CO2 supplementation to facilitate the metabolic rate, or move into a more temp resistant Sativa in the future.

I found Canna nutrients to have this problem in flowering myself and it took a lot of tinkering to narrow down on the problem. Veg is a breeze but in week 3-5 of flowering the cal-mag requirements shift and Canna just doesn't pick up the slack for some strains with certain environment. Get plenty of runoff and run the right ppm's of the solution through the container and they will recover.

The first foliar spray will actually stop the necrosis in its tracks. You will find that when executed intelligently, those foliar sprays can be a godsend to relieve quickly appearing nutritional issues.

And trust me man. You are not being judged. I was soooo much worse when I was learning. But that was another "life."

 

Reps to you bro. Amazingly detailed steps to help out a fellow grower. Awesome!

Beginning 3rd grow(Apprentice) - BC Big Bud

 

I was aiming for about a 0.6ec to a 0.7ec, so it sounds like the ppm reading is dead on. 78 is going to be okay as long as that humidity sticks around 55%, this keeps you in front of the problem.

Friday's solution should be somewhere around 600ppm aka 1.2ec. Things should be more or less back on track by Sunday.

 

I am glad everything is working out for you hombre.

How is she looking today? I am guessing some new growth up top and a little yellowing near the bottom. This is a good sign and with today's mild feeding you should get her right back on track and ready to be pushed again.

Monday is a new day!