Hi, these spots look quiet strange, it looks more like some corrosive substance has been spilled on the leaves. However your plant experience heat stress as 32 is a little over the acceptable temperature, try to keep it below 30C. Here is the DIY how to make air cooler
Ok back to the spots, it's definitely not the nutrient burn, so more likely potassium or phosphorus deficiency. With canna there is no need for any additives just use canna terra Vega and Floresa + some source of calcium and magnesium (I recommend plant magic magnecal) that's all you need. Canna boost accelerator does do a good job but is very expansive so it's optional. Start with 1/4 strength and slowly increase to 1/2. Never use full strength with chemical nutrients.