What soil r u using?
Also, what heat is it at max?
Looks like heat to me and why every three days?
Unfortunately the temp is too high.
Do the leaf edges feel dry/brittle?
Mist them regularly and feed with a good stress reliever after the heatwave is over.
Should be back in no time.
I swear blind by Rhizatonic in the early stages
yeah its very popular in the Canna range.
speak to your local hydro dealers and they will be able to advise you
Rhizatonic is in the first instance a root enhancer, but works well as a stress reliever too
afraid not..... it will not reverse the high temp through the day and subject the plant to a bigger temp swing
high 80's works ok for me as long as you provide enough ventilation & assuming you are outside....i think you'll be fine!