A question from a fellow grower:
what do you think my problem is?
This looks like a nutrient deficiency, most likely not enough phosphorus, maybe zinc. Check out this article How to Stop Phosphorus Deficiencies In Marijuana Plants - ILGM and if you start with and use a well balanced nutrient mix that was already designed with cannabis in mind you will run into less problems and your learning curve will be better as it will be easier to identify what may be going wrong with more things being standardized you are more likely to isolate the problem. http://www.marijuanabooster.com/
That’s right. When you realize you have an issue such as this; It is advisable to flush your plant’s 3 to 1 (water to volume container); then apply a fresh balanced nutrient solution.