Anyone knows what could Be causing It?
Leaves that are affected are pointing down, It Is spreading from the Bottom leaves to the top ones but currently only 4/5 leaves look like this.
Looks like it’s starting to have a calmag deficiency, that’s the classic tell tail sign when the veins of the leaves stay green and in between them start to yellow. Although we need a bit more information to be sure? What kind of soil are you using? Are you substituting a calmag? Nutrients? Autos or photos?
The lower, older leaves die off as the plant gets close to or is in flower.
This is a normal process with cannabis plants and something that can not be cured or prevented.