Hello Rafael,
With regards to the water, look through the articles as Deepin Peat says. But I thought I would state my method as I am quite a lazy fishkeeper and so things have to be easy!
I use a 50 / 50 mix of rain water and RO water. I use brown oak leaves collected from clean ground (clear of pollutants) and have recently started to use Indian Almond Leaves. I have had excellent results from these almond leaves. They are widely available; I buy mine from TA-Aquaculture.com at a reasonable price.
By the way, I used to use peat but it got too difficult to find in the UK. My method used to be to have one bucket with holes drilled in the bottom that would hold the peat and place this on top of an empty, clean bucket. Pour water onto the peat and acidic water would collect in the bottom bucket. Use leaves, it’s easier!!
Keep in touch with the forum and good luck.
Mark