Light cloudy green areas between veins

Since it is happening in older leaves, the nutrient is mobile. Spray it with epsom salt if it's magnesium deficiency.

Gota agree with Ezzjaybruh here. MG issue. little snip it on CEC https://www.pthorticulture.com/en/training-center/cec-cation-exchange-capacity-soilless-growing-media/ Good Luck!

You’re in a straight coco with hydroton which is infamous for issues because of CEC. It leaches mag from your feeds if not properly washed/buffered

Bruh. This is textbook mag deficiency

Going to disagree with my growmies here - this is NOT an insect problem nor is it a nitrogen deficiency... It's looking to me like the beginnings of a potassium deficiency for some odd reason. I don't know your nutes and they're not saying precisely what their NPK composition is so unless you've used this nute before, I would tend to suspect it as not having what the plant is needing in terms of the P and K.... Everything else looks spot on - you pH is perfect, your temps, humidity, you're giving them calmag, you've buffered your substrate .... you might just consider increasing the dosage of the All-in-One... Good luck...

It could be a few things, honestly. If you don't have a pest prevention routine, you may want to look into one. Better safe than infested and sorry! If you don't have a natural way of safely preventing pests, i have a handful I'd be willing to talk to you about. But, back to your question: It could be a deficiency, or pests. Some pests suck the life from your plants, some pests chomp on your plants. Either way, they're no good. So, I searched up a link that will show you what deficiencies cause what symptoms with your plant. Check the undersides of your leaves and see if you have any critters grabbing a free snack. Use a magnifying glass, if you have one. Some of them, like thripps, can be very small. Then, if your plants are pest free, check out the link i'm going to share. I recommend bookmarking it, or saving the pictures as a reference. It will save you a lot of time until once you have the symptoms memorized. Also, don't pay any attention to Nugz. He's a sour, lonely soul. If you're new here, please select the answer that helped you out the most by clicking on the "answer" button underneath what the person said. If you have any questions, feel free to message me on here. You can pull up your messages tab by clicking on the little airplane in a bubble. It's located on the bottom-right of your screen. I hope this helps!

I would say this far in, it’s a slight nitrogen deficiency. The plants take 1-2 weeks to show what’s wrong and 1-2 weeks to show that you fixed it. Looks like you are growing in coco and that’s a pure nutrient medium. Up the nitrogen and I think you will be fine! I’m a huge fan of alternating nutrient brands to get a mix of micro nutrients. Good luck. ✌️💚🌿💨