I ran into this problem and no one on this site was able to give me the answers that I needed. So I research it for several weeks trying to nail down my problem. I am also a first time grower so u can take this with a grain of salt if u want but I have 10 healthy plants that are currently in their 3rd week of flowering. I will attach pics of my problems and then pics of my healthy plants so u can see.
I came to the conclusion that my plants were lacking the nuitrients they needed and were having a calcium and magnesium deficiency. I got some CalMag and watered them with that for a week and then I started using the "lucas formula" which is a combanation of Flora Nova Bloom and Flora Nova Micro. Every few feedings I would also give it some Dyna Grow 7-9-5. You dont want to over due it with the chemicals tho because u could burn the plants with them. I would feed one day and water the next time. I prob fed/watered my plants 4 days a week.
When ur plant is deficient in nuitrients it will get stunted and stop growing. Thats what happened to me on 10/17/12 and I started giving them the CalMag and I saw an explosion of growth again on 10/21/12. Shit worked fast.

Here they are when they were sick...I fought the problem for almost the entire time they were veg
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Here they are now healthy and flowering
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ghost83 Reviewed by ghost83 on . ****1st indoor grow need help please**** ive been growing my plants now for about a month and ive ran into a few problems . my plants have been growing for over a month and are only about 5-6 inches tall i just really need help to figure out what problems exactly do i have and how to fix them and weather or not to start over im growing in a 4x4x8 tent with a 4ft 8 lamp flourescent fixture i have ventilation im growing in mg soil with no added fertilizer as i noticed the plants leaves getting yellow and only green on the veins and Rating: 5