Substrate

In general, for rooted plants: 1"-2" soil
Cap with 1"-3" sand, gravel and/or river pebbles to prevent from it being stirred up in the water. Research exact depths for what your exact plans are.

All soils provide a few years of nutrients. After that, it's generally recommended to
add "Root tabs" deep into substrate below the plants using long angled tweezers about once a month. Research!
Aqua Soils:
baked nutrient dense, soil granules designed for aquariums
Ultum Aqua Soil 10L/9kg/19lbs($70)
Premium, less messy than potting soil
Fluval AquaSoil 17.6lbs ($32)
Standard, less messy than potting soil
Miracle-Gro Organic Choice 15lbs($10)
Huge mess, make sure no added fertilizers, perlite, chemicals or manure.
Dig your own garden soil($0)
Huge mess, make sure no added fertilizers, perlite, chemicals, or manure.
There is risk and reward to harvesting from nature. Gather from clean areas in nature away from roads, pesticides and fertilizers. Research!

🏖️Many fishes/some plants need at least some sandy areas to express their natural instincts and raise quality/longevity of life: Corydoras, loaches, sand sifters/dwellers , it's generallyrecommended to use fine grain sand.

Compacted sand deeper than 2" may increase risk for pockets of toxic gas buildup. Sand like this benfits for aeration by trumpet snails, sand sifters or human poking holes in the sand.

⚪Light sand is pretty but more work to maintain beauty. Non-threatening but mucky algae can grow between the sand and the glass on the side of the tank.

⚫Dark sand may encourage some fish to shift to dark phase of their coloration.

Pick the grain size and color then rinse sand until clear before adding to tank, cheap sands are generally considered safe, but research any substance before adding it to the tank.

Gather Sand($0):
There is risk and reward to harvesting from nature. Gather from clean areas in nature away from roads, pesticides and fertilizers. Research!

🪨Smooth gravel & river pebbles provide a home for nitrifying bacteria.
For some plants rooting in gravel is easier than sand.

🟣🟡🟠Cheap colorful gravel may eventually chip off into the water. Nitrifying bacteria has trouble sticking to smooth epoxy color coating. Some fish react to colorful gravel by being less colorful themselves.

Gather gravel/pebbles($0):
There is risk and reward to harvesting from nature. Gather from clean areas in nature away from roads, pesticides and fertilizers. Research!