Eventually the whole thing had managed to reset by itself.
The most important factor are the fish - specifically Red Sword-tail fish.
They make sure there are no mosquito breeding in this little catchment.
Another factor are the sunlight - they are so limited.
The Vertical plants virtually had blocked most of it.
Most of the plant species didn't make it especially the big ones.
What appeared to survive helps to make sure
that the water don't get flushed out during the rainy times.
I may have to reset the whole thing.
Still looking out for ideas.