Yes the lights are irrelevant to this problem.

What is your soil mix? Have you checked your pH? Is there any peat in your soil? If so, did you remember to buffer it with lime?

The purple color.... what strain is that, is it a 'black' strain? If not, do your night temps get down below 65?

Remember that there is a combination of factors that is DEADLY to cannabis:

-low pH
-cold temps
-wet soil

Those 3 things together are guaranteed disaster.

Do not add any more nutrients until you have ruled this out. It will just make the problem worse.