Those plants are too young to be receiving any nutrients, especially if the soil you're using already has nutes mixed in. Also, if you're going to continue to use RO water, then you have to supplement the elements that have been removed by the purification process. Calcium, Magnesium, and Iron are the big three. CalMag+ is highly recommended. That's most likely why you're seeing the spotting, and the burnt/curled leaf tips are probably the result of overfertilizing.

Take care. :jointsmile: