Ah thats common. You See, those things you hold in your fingers are normally found on your plant - to find them in your fingers means you stressed the plant by ripping leaves off of it. No but in all seriousness :

There multiple deficiencies that i personally See in those leaves, Magnesium being one of them. Instead of going out and buying a whole lot of shit youll prolly Never need - try adjusting the ph of your water to around 6. the adjustment is to See if maybe your plant is locked out of nutrients.

thank you for your availability. I’ll tell you right away that I don’t buy random things. I fertilize my plants with the complete PLAGRON organic line: Grow/bloom algae etc… I always check the pH of my water at every irrigation, furthermore the soil I put is rich in earthworm humus, guano, perlite and a good dose of Mycorrhizal fungi right from germination. I detached that leaf immediately after both water and heat stress (the cooling system turned off while I was away, reaching 37/38 C° with 20% humidity for almost 36 hours! It’s a miracle that they didn’t die, you can see that they are F1 genetics. ☺️. in my opinion that is a light/heat damage in a dry environment. as you can see now they’re back to being nice and green. don’t you think?