Fert burn or K deficiency?

[AnomanderRake]

So do you still feed with every watering? How much and how often?

Right now I'm feeding 2/1 (two with Biogrow, one without).
But probably because of the high humidity (?) I only water/feed them every 4 days avrg... So since I created the topic I fed them twice and tommorrow is the first one without fert.

No, I didn't miss the perlite. And nope, it's not anything like hydro. And I suggest you keep your ph in recommended range, or you will risk nutrient lockout.

How are you testing your ingoing water and solutions?
How are you testing runoff ph?

I'm testing the ingoing and runnof with a digital PH tester... When the problem started the PH was 6.7 average. Now it´s 6.2 for one and 6.1 for the other.

The burned borders stopped for the new leaves but some of them have the very tip burned, but not spreading to the whole leave.