First time grow questions

I have 2 plants that I got as clones. (Afghans) I run a 315 Cmh light 18 on 6 off ( timer) aprox 2.5 ft from my plant. I only water when the first few inches of soil are bone dry. Filtered Water ph going in is about 6.0. At this time I have only just begun feeding with a small amount of tea compost added. The soil I'm using is an organic super soil made in michigan (dig it organic soil) I run fans so they dance a little. The only issues I've had thus far is keeping it warm during lights off. It can hit like 58 f at the lowest with a humidity of like 30. And I'm getting some browned edges on my leaves and my stalk is purple. I dont know what to think about this so I figured I'd ask here. Thank you. Getting a warm mist humidifier asap to fix the humidity, but dont think low humidity for a couple of hours would be a plant killer.

Sure that purple isn't a result of genetics?

Yah I was hoping to figure that out. I'm still kind of ignorant on this.

Go back to where you got the clones and ask. If they are purple by design you can then stop chasing that part of the equation. And while you're asking, ask about the general needs of that particular strain...things like do they like lots of nutrients, whether they're Mg hogs, etc...all strains have their preferences. Try to find out what yours are.