Why are these leaves marked and what can I do to get rid of it
This appears to be a fungal issue. I have a recipe that I recommend, which is safe, and natural. This will not harm your plants. This recipe is a broad range pest control for most insects, fungi, and bacteria.
The recipe is as follows: First, you will want to prime the soil with dolomitic lime, then spread wettable sulfur to Kill off any infection in the soil. I Also like to spray the plant itself. Mix a few drops of one or more of these ingredients into warm water with a spoonful of coconut oil: Rosemary oil, lavender oil, neem oil, garlic oil, cinnamon extract/oil and for really bad cases, also add clove oil.