You need to start feeding. I would immediately go with 1/2 strength Cal Mag Plus from Botanicare. That will help tremendously when you are using Distilled or RO water. You should also go ahead and start 1/4 strength of whatever nutrient regimen you plant to use. They are starting to get a little N deficient and would benefit again from Cal Mag Plus. I would go water-feed to start here because they look very hungry. Don't go very strong, very seldom, go with medium strength fairly often, they will love you for it.
Stay at each strength for at least two feedings. I wouldn't go over 3/4 strength until you're about 3 or 4 weeks into flower. Some strains can go full strength, some can't so it's better to be a little under than over. The plant will recover just fine from a little hunger, over doing it and doing too much will often jack it all up.