I'm already far in the process of making by own sand and gravel from ground from my garden or a nearby location (e.g. in order to avoid buying and transporting stuff over many kilometers that I can make myself or for aesthetic reason) (medium sand, coarse sand and fine gravel (= 0.2 to 6.3 mm) according to ISO 14688-1:2002) and already
- made sure I'm not violating environmental or property laws when aquiring the ground
- sieved the ground with two sieves determining the minimal and maximal size of grains
- rinsed the gravel multiple times (like I'd do for store-bought gravel)
- desinfected the gravel with boiling water and paracite desinfection (for living food)
I assume that the small remaining amount of biological particles will be destroyed by filtering and composting during the warm-up phase of the aquarium.
The only issue I'm having is to remove the carbon/peat particles from the resulting gravel. The particles are ugly and might cause the pH value to be instable for a long time. I figured that particles could be removed
- with an aquarium vacuum cleaner (from a bucket), but they repeatedly block the tube because peat is much lighter than the ground (but don't float all). The method allows very good separation with almost no loss of ground material and waisting of water, but is annoying.
- by crushing it in a mortar or mixer (probably one about whose look you don't care too much about and which can be cleaned easily). The progress of smashing the peat in the mortar is inacceptably slow and an average mixer without a sharpened rotor already destroys up to half of the sieved ground which is too much loss.
- by burning all organic material on a ceramic net on a tripod with a Bunsen burner. I didn't try that. I appears energy wasteful and expensive to buy.
- by removing the carbon with (bio-)chemical reaction(s). Those might take long time (since peat is already quite reduced to carbon) or intoxicate the ground, so they have to be chosen carefully. I didn't figure out any.
I'm looking for the solution which is both sustainable in terms of resource consumption and not time consuming. I don't plan to produce more than 10 kg of gravel.
 Not determining a minimal size causes infinitely fine grained dust to block filter or remain in the aquarium for ever which causes blur at every move of a fish or hand.