1st Grow: indoor photo RQS

Day 63, First Day of week 4 Flower: The ladies look good, buds are starting to form. I have two leafes that are yellowing on one plant (una). At the same timw the other leafs are darker than on the other plant. I think its too early to be natural fading, so i checked everything. I had 2-3 fungus gnats in the tent, so put in some yellow stickies. But i doubt that they are the cause of the yellowing. But something to keep an eye on. I think they can't be over- or underwatered. No Light or Heatstress, feeding was at 80% of the recommended schedule (so no nuteburn), windburn could not be possible, so the next easy guess is the ph is way off. The low leaf yellow indicates problems with N or P (mobile macros), so it has to be pests or ph. I don't think i underfed them with 80% of the recommended dose. I didn't want to test the runoff, because i just discovered a few gnats and didn't want to increase that problem. But checked the ph of my tapwater and it was around 8, which is way higher than the last testing i did (6.9). With nutes added the ph was 7.2. But because of the slight nuteburn last week, i watered partially just with plain water. I think there could be the issue and its good fixing that anyway. So i watered them today with ph controlled nute water with a 6.2 PH and we'll see what it does. Fingers crossed. Best case scenario would be that it is an early fading and no more leafs show yellowing (and i identified two potential problems along the way). Good lessons to learn. Day 65: The problems seem not to be getting worse, so thats nice. But i'm still sceptical. Going back to the full feeding schedule with the next watering and set PH at 6.0. Hope they'll like it. Day 67: Okay it is getting worse... Well Shit. Waited 4 Days to water again, to fight the gnats. Feeding day with 2l nutewater for each plant. Full on schedule with 6.3 PH. I'm kinda lost right now. The Gnats have not been spotted anymore, the stickies remain clean. PH is on, feeding should be sufficient. Guess i'll just wait 2-3 Days and watch how she takes it. Hmmm... It looks like a potassium deficiency (according to google). So with the full feed today, it should get better i hope (and pray). Day 69: Oh boy! They really look fucked up... So... the discoloring doesn't seem to get worse, but they developed rusty leaves over night. So new theory: As long as the water had fully added nutes, the ph was just enough to let them absorb some of the nutrients. But my caution about nuteburn led to watering with tapwater (without checking the ph) what led to a nutrient lockout which is now. So they absorb all of the nutes the could not uptake the last two weeks and now they got severe nuteburn. So i try to flush them with a lot of (ph adjusted!) tapwater and see if they get better. God i feel like such a moron. 🙈