Mold on my babies?

I've got ten plants growing in a 2x4 tray in an ebb and flow system.. The tray is filled and drained twice a day. The plants are about 2.5 months old, still in veg, under a 400w MH. I'm sure you can imagine how crowded it's getting in that tray...

I also have 3 girls in another smaller tray under a 125w CFL grow light. These three are fed by watering can once or twice a day. They're about a month old.

All the plants are in rockwool cubes, the ones in the main grow area are also in coir fiber in peat moss pots.

I have two possible problems..

The first problem is in the bigger grow tray where maybe 3 or 4 of the pots have this thin layer of white fuzz on the coir fiber (see attached pic). I don't know if this is mold?

The second problem is in the smaller area where the three girls have been neglected by my roommate (asshole!) for the past two weeks while I was away. He watered them some but definitely not enough.. these 3 are only in rockwool cubes, and the cubes were way too light when I picked them up today.. they were almost completely dry. The problem plant is one of these 3, the rockwool cube is completely green on the top (see pic) and white fuzz is growing on the bottom halves of some of the leaves. What's wrong with her?!

Thanks!!
Nick

I think you might be keeping the cubes too wet, that is algae growing on the cubes.
You can buy special caps which fit onto the top of the cubes to prevent algae growth

I try to keep them wet enough so they feel heavy if I pick them up... How would you recommend I water the plants in the cubes?

i don;t do hydro , but you could give them a gentle squeeze after watering. This may help

It is Algae. All uncovered, exposed to light rockwool get it. If left uncovered it really gets nasty looking. I used to put duct tape to cover exposed areas. Now I use Panda film. It still gets nasty looking but nothing like uncovered. Good luck.