I think the 1.0 EC was slightly high for the size of the plants, based on EC schemes I've seen and scribbled down on my formula sheet.
EC stands for 'Electrical Conductivity' and is a measurement scale for the concentration of chemicals in your nutrient solution. More at CannaConnection!
www.cannaconnection.com
An indicative EC range for cannabis plants is 0.8-1.3 for seedlings; 0.5-1.3 for clones; 1.3-1.7 under vegetative phase; 1.2-2 during flowering. Different varieties of cannabis might require significantly different values of EC.
You'll note your 1.0 value was not necessarily outside those ranges. Another set of ranges are found in Fluence Engineering's High PPFD Cultivation Guide. In Table 10, for cannabis, they recommend 0.3 to 0.7 for establishment, 1.0 to 2.0 for vegetative, and 1.5 to 2.6 for reproduction.
When I looked at your plants in an earlier thread, I thought the damage looked like calcium deficiency. I just checked them again, and it still looks like a good possibility to me.
I would try changing one thing at a time, and observe any changes over a few days. If your good plant begins to look sick, back off and restore older values.