After a good start in week 1 I started to experiment a lot with my grow setup. Due to my impatience I removed the lid of my cultivation box. After a few days I noticed a relative slow growth compared to the first week. My assumption is, that the relative humidity was to low (30-40%). I didn't want to put back the lid of the cultivation box (don't know why ... Im dumb :)). So I tried to bring back high relative humidity with alternative ways (wet towel, lower temperature, on/off switching of ventilation). Nothing worked really well so I finally decided on day 16 to put back the lid of the cultivation box. Simultaneously I raised the temperature (Day 25°C, Night 20°C) and raised also the PPFD from 300 to 600.
P.S. Sorry for the bad quality of photos. My smartphone has broken and I had to switch transitionally to an older smartphone which has unfortnunateley camera issues. Waiting anxiously for my new smartphone.