Cut lower leaves?

There may be excessive watering and heat Good luck my friend

Is there also a possibility of having rotten root?

You think? Cause a lot of guys told me that 4ml/L of fish mix is too much.

Also, big note. There was never a time that I had runoff water. Is it the time maybe to water her a bit more so she drips? Or maybe should I flush?

If there is a nitrogen toxicity, the leaves should turn dark green right? All the leaves in the lower area are turning light green. Isn't there a lack of nitrogen issue? I'm testing the pH with pH papers and they always are between 6 and 7, so I'm guessing there is not a pH problem.

I wouldn't start chopping away too much before you fix the cause of the issue. This is not just due to lack of light, it looks like signs of issues in the plant. I see you already posted about pH issues and underwatering, those can cause this, also look for signs of toxicity - 4ml/l is a really high amount of fishmix for an auto. I would wait for the plant to stabilise and then remove the very damaged parts, if you cut them off now it'll continue to kill even more healthy leaves.