I started Mortgage Lifter, Yellow Pear, and Sweet 100 seeds in Jiffy Mix at the end of March. Plants have been doing very well under 4 4ft fluorescent lamps until 3 days ago. The lower leaves (first "true" leaves) on several plants have curled up, dried up, and then fallen off. Most leaves have gone from greeen to brown/black, but a few have yellowed before falling off. Top of plants still look nice and green, but the problem is moving up to the next set of leaves. I was careful to sterilize by pots before planting, and as it's a cold spring these plants haven't left the basement. I have bottom watered using a liquid 6-4-4 mixed at half strength every third watering with plain water in between. I gave them a shot of 15-30-15 Miracle Grow mixed at half strength to up the phosphate. Thought about trying some Epsom salt for magnesium, but my liquid 6-4-4 concentrate already has 0.6% magnesium so I held off. I'm hoping one of you can identify what is causing this and what, if anything, I can do to save them.

A picture of a set of Yellow Pear lower leaves is attached:

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