Please don't pull the leaves off to show us, we need to see where on the plant this issue is occurring. To me, offhand, it looks like you have two things going on, N- and Ca-... no, three, I'm going to include a K utilization issue here.
I have not used the brand of coir or fertilizers you're using, so I can't speak to how to adjust them precisely. What I can do is explain to you how coir behaves so you get an idea of how to better handle it for cultivation.
First, it tends to lock onto Ca and K at a molecular level. This is why it's important to have your coir pre-charged. IIRC, Canna coir is precharged (and pre-rinsed! gotta to that before charging) so I think you should have been good to start.
The other issue has to do with
cal-mag supplements. I'm willing to bet that the brand you're using is about 3:1 Ca:Mg. This is too, too low a ratio in my experience. For coir cultivation 4:1 is a bare minimum, I prefer 6:1.
Because Ca is immobile, it must be laid down in plant tissues from the start, and needs to continually be laid down as new growth occurs. That makes managing Ca your most difficult task here. Gypsum can help by topdressing and watering in, but in my opinion you're going to need to add Ca in the form of foliar applications along with root drenches, so my advice is to get a product such as BioLink 6% Ca and add enough of that to the feedings to make your Ca:Mg ratio 7:1 (you're playing catch up here). This may make them too rich to go along with regular feedings, so you'll probably have to alternate, as well as delivering some Ca via foliar application of the same product.
Again, further guessing here, but I'm going to say that overall this plant needs more food, but I'm on the fence as to whether or not it actually needs more K, or if it just needs more N.
Give us more information to go off of here. We want to know lighting, duration, temps day and night, relative humidity, EC of feedings, and pH ranges.
Finally, you may want to go through my thread in my signature line "There's no such thing as a
cal-mag deficiency."