In veg your humidity should be about 65%, 35% is too low for any stage of the plants life. The lowest I am happy with is 45%, and that would be at the peak of bloom.
Are you checking the pH of your nutrients before you are applying them to the medium.
ProMix is not truly soil, it is peat moss and perlite, there is no nutritional content in that medium; soil contains minerals and organic matter that will feed the plant. Therefore your plants will only survive on the food you are applying. If that solution is not pH balanced correctly your plants will not be able to take up the food you are applying. For
ProMix I usually recommend people apply nutrients at pH 6.2-6.5, but I am not a
ProMix expert and there may be someone on here who could provide a bit more specific info about pH in
ProMix.
If you can't tell when the pots are dry then they are not dry. There will be a very distinct difference in a wet medium and a dry medium and you will 100% feel it. An hour after watering lift your pot, give it a lift every day until you can lift the pot with no effort, this is when you should be watering. Right now that could be 5 days, possibly longer, if your plants roots need to recover from being over-watered. But let the medium dry out completely; it is only too dry if it is pulling away from the sides of your pot.
As for the Skunkwerks, I had never even heard of it until you mentioned it. I do not know the quality of the product and what its guaranteed analysis looks like and what micro-nutrients it may contain or be missing. Also I don't like how low the ratio of phosphorus is in that bottle, it definitely feels like its not really going to be a great product to get you through the whole process. Regen-a-root is a good product but it is very low in actual nutrient content. It is a nutrient aimed at giving your roots a boost, but not so much the parts of the plant above the soil. So it is highly likely you are not providing your plant with all the nutrients it needs. I might suggest the Flora Nova line from
General Hydroponics. It is a high quality, organic based nutrient line (there is a grow bottle and a bloom bottle) with just about everything a plant really needs to thrive.
As for your purple stems, it is usually an indicator of stress on the plant. It can however also be a genetic trait. But don't focus too much on the purple stems.