Old fans yellowing between veins and at margins, n...

I agree with CannaSapiens. Adjust Ph. Let the soil dry out. From immoderate irrigation, the substrate is oxidized.

Hi there. Happened to me with the exact same strain. You could lower the ph a little bit. Remember: Different nutrients are absorbed in different ph scales. So ph fluxuations can mimic every kind of defeciency. 90% of the problems in not about what you feed to the plant, but its about the plant's ability to absorb it. Correcting your ph usually solves it and the damage deteriorates in the already affected leafs.

The new growth is normal, the affected fan leave looks like magnified nutrient water drops marks.

Hello Do you sometimes water on the leafs? It just looks like burn marks from water staying still on the leafs when giving water? Otherwise it can be chelated nutes in your soil. Maybe a flush here would do the trick. Give 2 times flush water. And the third time give a little bit of nutes again. Hope this helps! Kindly regards

Looks to me a Ca def moreso than a P excess. P excess comes with more yellowing towards the end of the tips and quick necrosis of the tips. Looks classic Ca deficiency to me. You know what to do. Your PH is a little high for my liking, I would lower it before adjusting nutes. but if 6.9 works for you, it works, just likely leading to the Ca lockout