Leave issue again :( can somebody help pls?

Ok, I reduced the EC to 0.7 and this was the first night the ph droped only from 5.7 to 5.5 and EC from 0.7 to 0.6. Added ph + to hold it at ph 5.7. Maybe the EC was to high. What do you think about this? Calmag issue in combination with high EC as root cause?

I use RO water

It's your water. If you are using tap water, this is your issue. Start using demineralized or RO water. Add 1ml/l of CalMag to the reservoir and you won't have any problems more.

The roots are clear/white and I cant see any sign of rootrot. I have lowered the EC from 1 to 0.7 and added calmag with the last water change. The ph is droping instead of raising.

Also I would check the root's, See if you have any root rot going on. They will be brown and slimy. Just brown is not always a concern as nutrients can dye them that color. You have to feel them to see if they are slippery. 100L should be more then enough to keep a PH balance.

It looks like a PH issue to me. Keep the PH at 5.8. don't ever let it go out of range of 5.5-6.5 if it does you will get this( which can show up a week after the fact ) Since your now adding cal-mag you look like everything is good. Take note of your EC every day at the same time( it will fluctuate depending on lights on or off ). If it is going down raise it. If it is going up dilute your water. Know what your plants are eating now what you "Should" be feeding them and that should help balance your PH. How big is your reservoir? You might want to increase the size if your getting high PH swings. Also you want to change your water once every 10 days max. Preferably every 7 days.