I am growing sum barney's vanilla kush and 2 died out of the blue, but the others are strong and big. I will just take clones from them and move on. Don't try to make weak plants grow they just slow down your other production. Get some fluorescent lighting and perk em back up.
What type of cfl are you using? If you are using just a regular cfl they just won't grow as well as a hps or hid bulb. Put them in with the hps or hid and put them about a foot and a half away from them 24/7 and plenty of air and low heat and water and they will spring back up.