White Widow Autos (first-time grower)

FINALLY got my Vivosun 150W light, so setup is now complete. Plant 3 looked like it was about to die (stem bending, brown/brittle leaves) so I germinated then planted Plant 4 as insurance. Plant 3 recovered yesterday after a good watering. However, leaves on Plants 1 & 2 started to look yellow this morning (nitrogen?). It seems every day has one problem fixed, but a new problem emerges. All plants look small to me, but maybe it's because they're autoflowers. I learned more about VPD and now try to keep in around 0.75-0.80 for the seedling stage, which is roughly 72 degrees and 71 humidity.