My current feeding water consists of:
1. 20 l of water
2. 40 ml of Canna Coco A
3. 40 ml of Canna Coco B
Leaves definitely show something is wrong.
What would you recommend to fix this?
Add some calmag to your feeding and you'd be good. From my experience seeing rust spots show up usually is a mag deficiency. Hope this helps your plants over all they look good. Happy Growing
First place to look is ph issues. Consider flushing with ph’d 1/2 strength nute water. Do you have just coco? If so next time maybe add 25% perlite as a lack of oxygen can cause nutrient uptake issues.