Hey whats going on im new to growing , but i been smoking a while but anyway im growing one indoor plant as of now im not looking for the worlds biggest harvest or anything because its my first grow and i dont expect to get mass amounts a few ounces will make me happy so my plant has been growing very slow it 2-2 1/2 months old and its maybe 6-7 inches 6 nodes looks more indica dominant , i use HPS 800 watt using some soil from a buddys who has a worm farm so not sure on the soil, but one day i go to bed and when woke up the stalk started to turn purple but the leaves continue to grow hesalthy and eveyday it looks darker and now the stalk is a very rich dark purple , its gettin thicker and stronger and its covered in tiny white hairs. so my question is when should change my light to 12/12 instead of 24/0 and should i be worried at all

Thanks.