Hi Giz,
you dont write much about type of soil or nutriets you have been feeding, which kinda leaves me at guessing.
my 0.02$: I notice two kinds of green on your leaf. This suggests to me your plant has been a little over fed too early. I'm guessing you have put her into a too hot soil or fed her too early too much.
The leaves with this double-colored green, are those which got created during time over-fed. They will naturally keep dying. It seems to me, the most new leaves are ok, so it means that now she feels fine.
Make sure your ph is right (ph = 6.5 +/-0.1), keep feeding her like you do now & you'll be just fine.
I also notice, that some leaves start to curl inside, this suggests to me lack of magnesium. You will soon find many leaves making a shape of a "boat", sort of canoe pointing upwards. It's MJ "praying" for Mg. Go to a pharmacy, buy some epsom salt, add 1 flat tea spoon per plant to watering can (dissolve it in water first). The problem will be gone forever.
much luck to you friend!