Are these underfed? Need help! (pics)

These babies were doing so beautifully, and now they are wilting and yellowing. I've been careful not to overwater, and only fed them once with a mild solution of FF Grow Big. Have I been neglecting them? My water/soil runoff is roughly 6.8 or 6.9.

http://i28.tinypic.com/10dhyqh.jpg
http://i29.tinypic.com/2dhybtl.jpg
http://i27.tinypic.com/307t4k2.jpg

Too early to feed. Wait until the 5th set of adult leaves is unfurling to start on a 1/4 strength grow fert.
Next time they need water, use plain tap water and water until it runs out the holes in the cup.