How many gallons is that pot? I think youre using too little water too often but the ph3 can also be the reason. I agree with BigBlonde, whenever my plants look like that I know Ive been watering too much. Your pot has way more water retention potential than the water youre using, your readings come on the dry side because your only wetting the top part of your soil but probably too much. Also at ph below 4,5 is toxic to your plants and also makes undesired metals like alumina water soluble which are also toxic for your plant. Ammonium is also absorbed in higher quantities at a time with a ph below 4.5 which would explain why I see a slight curling in some leaves (the ammonium nitrate, too much nitrogen being absorved too quickly). How many times per week are you feeding them? One? Also it looks like a photoperiodic plant to me because all of the growth and the fact that it didnt start to flower yet after 6-8 weeks.