Leaves getting dark brown spots, yellowing and getting crispy

Thanks for your replies everyone! As suggested, I started a diary, though it's probably lacking in data, since I didn't take any pictures so far and the site won't allow me to create a week without a picture. Sorry for that. There are better pictures in the diary than the ones in this post, as well as the nutrients I've been using and the pH value of the nutrient solution, so I hope you'll be able to get a better idea of what's happening. Any advice is appreciated! :)

En los cultivos con led debes agregar al agua de riego cal mag, pues este tipo de iluminacion lo demanda, te recomiendo el de Grotek pues tiene hierro y este hace que la planta asimile mejor el calcio y el magnesio

First, listen to Granny and start a journal to provide us better info to help you. Second, take photos with the flash forced on. This will give us better colors to try to diagnose the issue. Given the description and what I can see in the photos, assuming you didn't strip off all the fan leaves, it could be nutrient burn. The solution, if that's the problem, is to flush the pot with plain water to rinse excess away. Good luck and keep us updated.

It looks and sounds like you've got some issues with your nutes or your pH or both ... but beyond that, there's no way we can really help out here since you don't have a diary and all we know is how old the plant is. Start a diary, mate, and then ask your question again... Good luck!