Hi Jacob, I use oak bark extract to reduce the pH value.
For humic substances i use Humin Aktiv (Femanga. You can buy the products at pet shops. Both are natural products.
I use RO water from the Drugstore (10 Liters for 3,50€)
I use leaves of beech tree. I collect them in the autumn and dry them.
Bevore I used this i pour over boiling water.
Where do you come from? I live neer Ausburg, Germany
Greetings Hendrik