Is this Nitrogen deficiency?
I am about to be in third week of flowering (Day 42) on my outdoor autoflower. To this point, no nutes just growing in FFHF on top of FFOF. Should I start to feed nutes this late in the grow?
In quality potting soil your water pH is less critical than in hydopoinics as the soil and additives provides buffering. That buffering does has a limit though and you might be reaching the limit. I adjust my water to be 6.5.
I am not impressed with Happy Frog even for seed starting as I have to add nutes pretty early. Ocean Forest is much better but I still add low level nutrients sooner than most recommend. If you haven't given any fertilizer yet I would start. And of course pH your water. I give a low dose with every watering.
Are you PHing your water? that might be the issue. what got me thinking is the tips leaves, thats a sign that your plant isnt intaking. Check your water and add some food but do it in small amounts.