Nutrient deficiency?

Straight off the bat, you're feeding WAY too much... at 3 weeks, you should only be using 1-1/2 tsp of Canna A and 1-1/2 tsp Canna B per gallon of water!! NOT 8!!!! I haven't checked the other odd conglomerate of nutes you're giving her but where oh where did you get this mixture?! Canna is one of the best nute lines you can get - read their instructions and follow them! When you've got a few grows under your belt, have figured out what works and what doesn't, what needs improvement, then you can go start fiddling around with adding this or adding that... but right now, you are COOKING your plants and stressing them out. Here's my recommendation: FLUSH. You don't indicate what size pot you're using so I'm just going to explain this procedure assuming you're using a 3 gallon pot for each plant. Run NINE gallons of ph'd water through each pot (3x the water as the number of gallons of your pot). Into the last gallon, add .75 Canna A, .75 Canna B, .5 tsp Canna Rhizotonic and .5 tsp Cannazyme. Now let them dry out completely before giving them Ph'd water again. This is a link that will take you directly to detailed instructions about how to use Canna, in what amounts and when... you'll have to convert from milliliters to teaspoons but that's easily done by googling "volume conversion," setting the calculator and punching in the number of ml they're giving you here. And put that other nute stuff on a shelf somewhere for POSSIBLE use in the future. For growing in Coco, you are at the high end of the PH scale.. don't exceed 6.0 and don't fall below 5.5. So good luck - and I KNOW you can do this! I love your enthusiasm and your desire to grow great weed - but sometimes, less is better! :-D