Betta Fish: Modifying my first tank

This is my first ever tank and my new betta, Riciu.
I've had this tank for about 3 years and, in that time, even if I moved the scape, added and removed plants, the substrate remained mostly the same. It was also the home for two bettas, Casper, which died because of my inexperience, (probably) stress and improper maintenance. My second one, Zoe, received proper care, but developed tumors after a few months. After that, I took a break from bettas and focused on bigger aquariums for a while, without disassembling the tank. In the middle of July, however, I saw this one and hoped for better genes this time. Time went on and some changes occurred, but nothing seemed as urgent as the damage on the top fin, so I decided to redo the scape for good this time, changing even the substrate, as the first layer was simply too thin and the plants weren't doing so great without adding ferts, offering little consumption of the waste. I kept the filter, water, a small part of the old substrate, and half of the added layer of sand was taken from another aquarium, so cycling was not an issue. Now I added proper wood decor, a cave made out of coconut shell, and almond leaves, as the pH and hardness were a little too high ( I use water from a local source that we use for consumption as well ). Half a week has passed and even the overall mood of my fish improved. He seems more vigorous, more active, without being agitated or stressed. He simply waltzes around more often. Even so, I wanted to share this journey and ask for opinions or advice, if any comes to mind. Thank you