A Magnesium deficiency can cause purple stems. Heat or especially cold can trigger this, as far as the lime-colored leaves this is normally a problem with iron, and after looking at your ph you could be having a lockout. The ph should be between 6.0-6.5, also if you want to help the auto flower you can switch to a 12/12 light cycle I've had to do it plenty of times to help out autos, they just do this sometimes.