Please Help me Help a Friend.

2 times a week seems a little short to me. Rain water is supposed to be the perfect PH. There’s definitely deficiency issues. I personally would feed 2L every other day per plant at that size. Definitely look in to some sort of nutrients or organic substitutes. I tried to cheap out in my first grow and had nothing but issues from week like 4-7/8ish, then decided to sack up and invest in nutrients. They can be pricey, but for the amount you use per feeding its really not terrible. Im still on my first 1L bottle of each nutrient 4 grows later as you only use 2-10ml of each per feeding.