I started one recently and so far so good. Used water from an already established aquarium which probably helped speed things along. Just three types of snails right now to keep it going but will be adding some mountain minnows next week.
I love your videos. I did a sinilar thing to u, but far less beautiful. I used a big rubber concrete mixing bath thing and covered the bottom with sand. I added floating water Hyacinth and aquatic plant hornwort. I kept this outside in semi shade undercover. This worked amazing well as an ecosystem and the water stayed crystal clear, no algae, for many years. All i did was renove some plants when tbey grew too much. The water used to top up from the rain and there were small drilled holes for drainage around the top so it never overflows I kept a large albino softshell turtle, several lace / pearl gorami and giant ramshorn snails in there Also wild animals appeared aa a surprise like freshwater shrimps, assin snails. Pond scaters and various aquatic worms
I don't think there is a big difference between using sand or gravel. there are other more important details that can influence the health of the ecosystem
