Deficiency or something else?

NOT a deficiency, this is burning from excessive nutrients...........stop feeding as much as you have been! It is NOT a cal/mag deficiency!

Hey growmie, yeah you’re not far off — this really does look like a cal-mag issue, but it’s probably more of a pH + nutrient timing problem than a straight-up deficiency. Coco needs stuff to be available fast, and the organic 4-4-4 + 2-8-4 you're using is just too slow to break down, especially once you hit early flower. Add bat guano into the mix (which also takes time), and your plants are basically getting underfed right when they’re asking for more. Now throw in a bit of pH drift — if things dropped under 5.8 even briefly, magnesium and calcium start locking out. That’s where that weird rusting and edge damage is coming from. What I’d do: Give a small shot of liquid cal-mag or top-dress something faster-acting. Make sure your pH is locked in at 5.8–6.0, even with organic inputs. Maybe skip the guano next round unless you compost it first or run a longer veg — it's good stuff but lags behind in coco. No need to panic though, just tweak the inputs and she should bounce back. New growth will tell you if you’re on track.

Hey there don’t worry it’s an easy fix sometimes when your soil ph gets off and is to low when your plants start to flower it starts to put them into lockout and they can’t absorbs the nutrients they need If you don’t think so what the plant some and check the ph if the water that comes out the bottom the pot You will see it’s low down below 5 or close Just take the plants to a bathtub and run 5 to 10 gallons of tap water thru the soil most tap water is oh 7 to 8.5 this is fine it will. Bring the oh back up to a good zone After washing soil out with tap water make sure to give plants a few cups of water with nutrients all that tap water will wash out most the nutrients you have in the soil Good luck

gaia is also short on cal mag especially in coco. i had to get a cal mag supplenent even in soil. but yes i have experience it. uprising foundation or elemental is what i ended up using to correct it.