Well it's not a temperture problem then.

3 part GH with no extra crap seems reasonable. Which BTW should provide enough nitrogen for the plant's growth.

I looked thru a horticultural textbook, and blue stems is not mentioned as a symptom of nitrogen deficency.

I'd probably like to see a slightly longer dark period, but I doubt that would cause purple stems/slow growth.

Since we are playing 20 questions, let me ask you this; are they all the same strain? What strain are they?

OM