Advice - White spots and dark leaves on cornflower
Beginner gardener here. I have been growing cornflowers from a pack of seeds and soil bought from a supermarket around 5 weeks ago. They were growing really well however recently don't look so good. Some leaves have turned a reddy purple and white spots have appeared on the majority of leaves.
They are in the garden, in direct sunlight. I've been watering them every day with tap water.
What is wrong and what should I do?