Yellow leafs on seedling 2 week old

Hi! New grower here. On week 2 after seed planting. I am growing 3 Blueberry and 3 White Widow from seeds. Had 100% success germination! I started seeds in glass of water for 28 hrs then placed in Jiffy pods in grow dome under T5 lighting, I removed dome after sprouts appeared, when tap roots appeared from underneath the jiffy pods I transplanted into 2 gal buckets with growing medium Cocoa coir and peralite in bottom 2" that’s where my drainage hole is.
I then put all 6 plants underneath 1000Watt HPS lights with reflector hood and I have the light about 18" above plants. I started the electronic ballast at 50% setting then yesterday I turned ballast to 75%. I keep the grow room at 75-80 F with humidity at 40-45%. I have a floor pedestal oscillating fan 5-6 ft away from grow table set on low with slight upward angle to circulate heat and humidity. My portable heater is behind the fan. I have 4 really healthy looking seedlings (1 white widow was injured & didn’t recover) 1 of my blueberry seedlings leaves turned all yellow with a little green in center(veins) for 4 days now. It gets the same nutrition as the other seedlings, 50% diluted FloraMicro 5-0-1 FloraGrow 2-1-6 and CaliMagic 1-0-0 per 1 gallon water that’s ph 6.0. I have only given nutrients twice so far,second time last night, H2O once in the 2 weeks, as the soil has stayed moist 1 knuckle deep. I lightly spray 3-5 squirts of water to leaves twice a day. Why is just 1 plant displaying possibility of nitrogen deficiency but not the others? Or is there something else going on? I have downloaded your grow manual and read it religiously over and over, which I give you credit for my 100% success in seed germination. Thank you for your vast knowledge in growing and for any help you may provide me. Cheers!

Green veins with yellowing could also be a sulfur or maybe zinc deficiency. It is hard to say why only the one is showing these problems when they are all getting the same mix. It could possibly be a phenotype thing in that one plant and as it is a genetic thing, just the way the DNA recombined when the seed was made that made that little one a little different and more sensitive to certain nutrient imbalances.

blueberry seedly

Here’s what my blueberry seedling looks this morning. After feeding mix last night and turned up lighting to 75% shes looking healthier with less yellow. I’ll keep an eye on her and see how well she recovers. Thanks for the answer!