6 weeks old leaves are distorted and appear discolored in some areas please help

my 4 plants are 6 weeks old and approximately 10 inches tall. they are master kush seeds i purchased online. they are under a 600w metal halide light approximately 26" from tops of plants. i run this light 24/7. the temp in the room is a steady 80 degrees and my humidity is between 40 and 50 percent some times it drops to 30 if i dont add water right away. my ph is at 6.3 and i change my water every 7 days. i use distilled water everytime i refill. i use a ebb and flow hydroponics system that waters my plants 3x a day for 30 minutes on a timer. i use general hydroponics nutrient solution. floragrow floramicro and florabloom. i add exactly what the bottle says to add per gallon for my 7 gallon resevior. i noticed these spots on plants a few days ago and they are getting worse. some of the stems are a alittle purple also but otehr planst are green. please help is it nurtient burn or is my light to close? are there any other nutrients you guys would suggest i use or add?

Use less....I use same system but at half strength. pH is a bit high- 5.8 is ideal for hydro. Using DI water, you may also run into a Cal/Mag deficiency. I had to back add untreated well water to boost minerals to 100 ppm before adding nutes at 500 ppm. I got those spots and cal/mag was the fix for it. Calcium phosphate and Epsom salts or cal/mag drench