Yellowing leaves during early flower

Hey all. Having a mini-freak out over some yellowing leaves. It started week 1 with fan leaves under the canopy going yellow. Now in mid-week 4, and everyday I open the tent, I’m seeing this progress to the top of canopy. I know this is ok later in flowering, but just seems to early in week 3-4.

Growing OG Kush, all organic, except for the ph up/down, which has been General Hydro. (Still confused on whether or not to ph water for organics??). Been PHing to 6.5. Last time I checked runoff, it was about the same.

  • First week of flower, I top dressed with Coast of Maine fish bone meal (1/4 cup) with npk of 5-13 0, 18% calcium.I also top dressed with some worm castings.

  • week 2, just gave Growganica’s Kelp It Real.(0-0-14) This is water soluble organic fert.

  • week 3 started with 1/2 cup Fish Bone Meal, top dress of worm castings, and 1 Tbsp Liquid Squid (2-3-0).

  • week 4, started thinking this is a magnesium deficiency. Especially because at the top, the yellowing seemed to happen under the LED. (Mars Hydro 2000, 28" above @ 75%. These girls are sensitive to light!) I didn’t have Epson on hand, so I gave 4 ml of Bloom City cal-mag. Also, threw in more Kelp It Real, and worm casting tea.

Any thoughts?
I read OG Kush is a heavy cal-mag feeder. So, was thinking not enough magnesium. But calcium should be good from fish bone, I would think. I also use Carbon Filtered water, so the cal mag in that water should still be there, after filtering.
The other thought is maybe not enough potassium?

Here are some pics:

Oh, also, I am growing in 5 gal. fabric pots. The two having this issue only used Happy Frog soil. The 3rd plant, pictured below, is not directly under light, and was 50/50 Happy Frog and Ocean Forest, and is not showing this deficiency at top of canopy. Although, under canopy is still aess of yellowing and dying leaves.