RQS Quick One - 2nd grow

The plant is growing like expected, I'm adding about 1 liter every 2 days. Humidity is a lot lower because I'm growing with an open window now (the tent is still light sealed, but this way the humidity can get out of the room). Temperature is around 24-26 degrees celsius, mostly because it's pretty hot outside this week. I stopped doing LST on the top because the main branch got too hard and I didn't want to overstress of damage it. I continued tweaking the side branches, getting a more wide plant. To my surprise, halfway this week flowering has started. I guess you can discuss if this is some sort of pre-flowering or actual flowering, but you can see it on the tops and lower down the plant. Now for the part that stressed me a bit: Earlier this week one of the leaves suddenly looked bad (5th photo). The leaf turned partially yellow with some burn/dry marks. It's a different kind of look compared to when I overwatered. My own suggestion is that this might be because of the nutrition I've added, but I'm too inexperienced to tell. Feel free to share your suggestions or answers to this. Some (3) other lower leaves turned yellow as well. But this happened last time as well. I guess this is partially because they get less light, and with flowering starting the plant might shift it's energy from leaves to flowers. In general I'm not worried because the burned look is limited to one leaf and does not seem to spread. I'm careful with overwatering, and I'm not adding extra nutritients yet. I'll also spread that nutrition over 2-3 watering sessions to prevent giving it too much at once. The plant is now 37cm soil to top, but with LST I bended it at bit so it's a bit lower than it should be. On the positive side: most of my side branches are kinda similar in height and much wider compared to my first grow. If all goes well, The flowers on these branches will develop equally and hopefully with more light going to all of the buds, generating a bigger yield in 2 months.