healthy plants went from good to worse. any advice or clues what do? thanks

heres a couple pics of the my lavender batch. one of them started dropping then became limp and lifeless and is going to die it looks like. anyway to save em when they get like that? also another started doing it today and im worried. is ther anything i can do. we are about to put them to flowering/ transition stage. any help?

thankkks?

36- 5 gal buckets in two seperate 3x6 rows (same room)
running hydroton with Hydro farm nutes
air stone w/sub pump w/tubing etc
55 gallon res (filled to 40-45 gals)
2- 1000 lights 1- 1.5 feet above plants
all walls sealed with reflective white mylar.

heres where im at,

put in 12 lavender on 3/4/2010

so far on the aggressive growth stage of nutes (4th stage) about to move to flowering stage next week and move them to another room.

water is a day over due could that add to my problems? about to change it..

What's the ph of your water???

like between 5.8 and 6.3 tops

How much aeration does your water get?

theres two bubbling stones. how much should a 55 gal have

what kind of air pump do you have, and how big are the air stones? and how strong is your water pump, sorry for all the questions, it's just hard to diagnose this, everything looks up to par so far!

250 wate pump. gals an hour

What do the roots look like? On the unhealthy plants your rockwool cubes are completely covered in algae, and on the healthy ones they are not. It's usually a good idea to cover those cubes up, my buddies that are using the same medium as you use small squares cut from garbage bags. Check your roots and see if the algae growth has spread to them. Also want to check and make sure your buckets are getting water to them. They look like they aren't getting water.