What could've cause this to happend?

One week into bloom.
The plant is taking up nutrients, water smells ok, roots looking fine.
I need a new PH monitor, but never had problems with PH before with the same usage of nutrients I gave the plant now.

Any ideas?

It might be a couple of things. The burns around the leaf edges are usually a potassium deficiency, but you’ve got it across most of the leaf surface in a few spots. Plus it usually looks more “burnt”; yours look more like they changed color on the leaf edges. Some burns on the tips too. It’s not just the top foliage, so it’s not light burn. They could be a deeper green color, how much you feeding. You said the roots look good, you in hydro?

This happened to me my first time hydro.
And right when I switched to flower. My ph was 9.4 lol. I hope I helped at all with that

Not saying that’s what killed it. We’re talking over 10 years ago. But I remember my ph was stupid fucking high when I went to trash everything

Agree with potassium deficiency.

I ran out of my AN Jungle Juice series which i've been using for years without any problems and had some AN PH-perfect that I hadn't used for vegging this plant.
I was away for a week, opened the tent the plant had grown much bigger but a lot of leaves was drying up and looking shitty.
Changed water with PH-perfect, checked the EC when it was time for that and saw that it was low even though I used the same amount I use with Jungle juice series.
But apparently PH-perfect is much "weaker" so the plant probably didn't get enough.
Sucks because you have to use a shitload from the PH-perfect to reach the desire EC and most vendors don't sell Jungle Juice series anymore...

The leaves that are dmg wont recover but all the new leaves looks much better and the plant seem to have recover now that I got my AN Jungle Juice back.

I’m glad she’s doing better for you.