Two week old plant having problems. Water Hardness? with pics

This is my first attempt at hydroponic growing. My first group of plants are about 2 weeks old from seeds. Out of 11 most look very healthy, but 4 and in particular one have several negative symptoms. Below are pictures of the worst plant, with some plants in the background starting to show problems.

It starts as a yellowing of leaf edges and very slight upwards curling followed by full flushing of yellow and downwards curling then finally brown dead spots.

With some research I first thought it was over-watering, so I added vermiculite to the coconut fiber medium but the symptoms continued to worsen. Now I am thinking it could be a problem with nutrients or water. I used Miracle Grow 30-10-10 in a 1/2 dose and MagiCal calcium, magnesium, and iron supplement (Coconut fiber tends to lose calcium) for the initial two weeks and now I have removed the Miracle Grow. Below is the analysis of my water:

Nitrate: 40ppm
Nitrite: 0
Total Hardness (GH): 300ppm
Total Alkalinity (KH): 160ppm
pH Level: 7

I do not think this is a light issue, I am using 6 T5 vegetative fluorescent tubes 4" from leaves 21/3. Temp 28C. Unsure of humidity. Ventilation and air flow good.

All help and suggestions are greatly appreciated.

As a side note, do these plants seem a bit small for two weeks? They are 3-4" tall.