SkunkXL Third Grow!

So another week has passed, and this grow keeps us puzzled. The previous issues seem to have disappeared, and now something else is going wrong. For some reason the plants are growing very slowly, and the back left plant is looking really bad. Very light colored and drooping leaves, and the stems are colored as if it is very stressed. One of our theories might be the CalMag being out of date, since its coloring has gone from dark greenish to black, but we still used it. We ordered new one, and will soon see if it makes any diffrence. It's most of all weird, cause all our plants get the same treatment, but they show very diffrent signs of health. We started feeding since yesterday, so hopefully the new nutrients are going to help them along and improve their health. A bit frustrating how rocky the start has been, hopefully we either find the cause or get an idea of what it has caused it so far.