If its a cal-mag lag why a RO water will fix that ? Suppose to have cal&mag in tap water.
Calcium in tap water is actually too large for the plant to absorb. It can cause a "blood clot" type effect, stopping the plant from absorbing nutrients. Looks like cal-mag def or nitrogen "burn"...didn't really look at the pics too well. I would say cal-mag. If you are using tap you may want to add a couple teaspoons of Unsulfered Organic Molasses at every feeding. The sugars feed microbes in the soil and help a lot. Also if you are not on a microbial tea you should be. They break down a lot of things in your soil to be easily taken in by the plants. Another thing with tap water is that most nutrients are made to be mixed with a certain amount of calcium in your water (ppm of like 120, but I'm no hydro guy and I don't test ppm) If your ppms are too low it could be locking out most of your nutrients when you mix. Some say to add Cal-Mag first because of this. PH can lock out cal-and mag as well. Epsom Salt is a way that old schoolers take care of Mag deficiencies.
when in doubt test runoff or soil ph ( i do runoff ). Flush if too high/too low. Distilled water just to be safe. at least 3x's that of pot size. Foliar feed some cal mag a couple times a day. If not better by the time the soil dries, hit it with some Epsoms salt, or cal mag, or molasses and pray.
....It may be PH of the soil also. Soil ph raises with nurtients after a couple days. you may be able to save the 4 plants on the outsides but I think you will probably lose the 2 in the middle. If not they may be stunted or severely stressed. Root rot you can battle with peroxide for a little while. Most of the time it wins very quickly. At that point you just try to Noah that shit and save the genetics...ie clone what ever is the healthiest and highest.
I would say that light poisoning from an led would be down the list very far. UVC is only type of Light radiation toxic to plants.
A good way to test your soil is to give them straight water (tap, r.o , distilled, doesn't matter) and watch the color of the run off. If it's brown, really dark brown, like coffee or strong tea...keep pouring until it's not. I would say you are in for a battle with what ever's going on with them. Best of luck. Good thing these plants are designed to survive. They aren't dainty and can take a hell of a beating. I live at almost 9,000 feet in colorado and I've just left these leftover clones that I gave up on outside, They are still kicking after 3 months with no nutes, no new container and the only water they got was rain. So they can take a lot of abuse and still keep doing what they do.
Molasses tip.
http://www.vitacost.com/wholesome-sweeteners-fair-trade-organic-blackstrap-molasses-32-fl-oz-1?csrc=GPF-PA-Foods & Beverages-012511700003&ci_gpa=pla&ci_kw=&ci_src=17588969&ci_sku=012511700003&gclid=CjwKEAjwkMWgBRCJ1L_wypbX0wkSJAC3Xio2jxK09MdZW1FJHLJ8S4NVB0WirsReKafhuE5jzMJD6xoCAlbw_wcB