Don't listen to the people saying it's the cmh, it's not. I think you might be running too weak nutrients, you said you use max 1.6 ec during flower right? I think Canna's recommended schedule is much higher than that. Maybe someone with some Canna coco experience can tell us what your ideal ppm/ec should be? I've never used that line but from their nute schedule they have you starting at 900ppm going up to 1540 ppm during peak flower-of course, you're right not to blindly listen to their recommendations, I would see what others are using for that line. I could be wrong, I just skimmed the answers, maybe someone else already mentioned it?