I'm curious about the purple stems too. I compared with a few others that are, or have grown, this same cut. They also had purple stems at this point, although it seems more pronounced on mine.
I've been feeding double strength Calimagic for a couple of weeks now and it does not seem to be making a difference.
I did drain and refill my reservoir this morning and upped nutrients. Previously I was sitting at 1.8ec and I raised it to 2.1ec. let's see if that makes a difference....
As far as the net, that's just an Amazon net. I order a few at a time and consider them one time use. I cut them up when harvesting.