sorry I meant this one https://www.parosphromenus-project.org/en/sentang.html
Oak leaves are fine, but not too many at the time. And its also true for the almond. If old they may not give off so much, but still add some of the valuable humin. But definitely go slow with those.
Its just that your tank looks like it has some ‘stony’ things 🙂 .. and I also wonder about the gravel, what is it ?
Sometimes I think that even in soft water, if you have some stones or gravel it will make whatever you do concerning ph very unstable, because the stones might draw the ph up again immidiately after you have lowered it, – and this will give a very unstable ph situation.
So … are you using soft water? and how are you lowering the ph ?