For a plant to stop growing completely is very bad. With this kind of plant, if it is not growing it is dying. Most common problems for plants to stop growing is too much heat or ph imbalance. If you share more about your setup or describe more what your plants look like (strange colors/spots), I might be able to help you. Do you have proper temperature control and ventilation? Do you test your water's ph before you give it to the plants? If you have a recent picture that would be even more helpful. I'm getting pretty good at looking at a sick leaf and recognizing the problem. Don't worry, nobody has a perfect first grow. I had my share of problems too. As long as you can get the plants healthy before putting them into flower, you should be fine.