ok I know how to solve your problem:
Number one: Take a deep breath and dont't freak every time your plant gets a little droopy. (I personally beleive) that plants of all kinds emit and recieve energy, and your negative energies arent helping.
number two: Do you know why they call it weed? because it is classified as a WEED! they may get a little fucked every now and again but they will continue to grow.
Purple stems at this stage are completly normal. as your plant matures if it continues having purple stems it could be a nute deficiancy and it could very well be you fell into a "purple" strain.
Ph testers are like 2 bucks. get out on the street and suck some dick.