That was my thought, that possibly the light was bleaching the leaves. Just to be safe you might raise it up a bit more, say to 24" and see if it makes a difference. If you have some cal/mag supplement you can also give them a foliar spray with it, mixed at about 1 teaspoon per quart of pHed water. Some of the early 2011 models of the GrowLEDHydro 290 watt LED lights had bleaching issues and the cal/mag worked well in those situations.
If it needs water, by all means give it some. But just plain, pHed water. What is Vitalink? I did a quick search and did not find any information on it.
If it looks like it's getting better just give it a couple days and see if it improves. Outside of the yellowing they look healthy.