Green leaves but droopy stem and leaves

OK, so I came home after being gone only six hours and this is what my plants looked like.
I don't have a before picture, but they matched pretty well what I had seen as a healthy plant. Now they are all drooping over.
There is no brown spots on them, but they felt dry. The temp has been a steady 77 Fahrenheit until it spiked late this afternoon, one of the fans got blocked.

Also I had adjusted my PH last night to a good 5.5, as close as I could get. I checked again today and it was up to 7.0, but I already brought it back down. I just want to know what could be causing this drooping and dryness in the stems.

Of the 4 plants total, 3 are effected, while the forth seems oblivious to the others' struggle. They all are getting oxygen from airstones, this is DWC by the way, and the lamp is MH, (400 w) and they are all about 7 days old.

an hour after adjusting the ph and pouring a little water over the cubes that it doesnt look any better.
I would appreciate some help in diagnosing my problem, I really dont want to see them die! THANKS.







the leaves seem droopy, i swear, my camera is just really bad.

Also it has been 7 days since they were planted in rockwool, and from looking at other peoples plants, they are growing very slow. They were in a rockwool tray for 6 days and were then moved to the netpots a day ago with the level of the water about 1cm below the rockwool. Why are they growing so slow?

A guess; not getting enough water?

Where there roots poking out of the rockwool when you transplanted to the pots?

Yes there were roots sticking out, that was when I decided to move them to the netpots. I was told to keep the water level 1cm below the rockwool, so it would be hydrated.

Honestly I have no idea how much to water them but it doesn't seem like I have a choice if I am relying on the bubbles to pop and hit them, seems like that would cause over watering. Leaves are not dried out

Well 3 of the four plants are completely dead after one night.

did an autopsy, and the roots had in fact grown about an inch out of the rockwool.

It just pisses me off how much research I did. I did all the right steps. The seedlings were fine, then after a day of being in the netpots they are dead.

any ideas at all on why this happened? one plant is seemingly unaffected.