Which chemical reaction to use to remove carbon/peat from sieved earth/gravel? I produce gravel for my aquarium by sieving and rinsing earth from my garden. After boiling and disinfecting it (with a solution against parasites) the rest of the organic material are composted or become invisible duff inside the gravel during the initial cycling of the aquarium. The only thing remaining visible are peat and other carbon particles of the size of the gravel which I currently need to remove mechanically.

Is there a way to remove them /shrink or reduce them to small pieces with a (chain of) chemical reaction(s) which


can be performed with a maximum of chemicals and equipment which can be bought at a supermarket or building supplies store
doesn't harm the fish after introducing them into the aquarium some weeks after the treatment - both through toxines and an instable PH value (more than +/- 0.5)
leaves the color and the size of the gravel untouched because my motivation to use custom gravel are mostly aesthetic and reducing the size would risk to block my undergravel filter (has a filter chamber with a separator for gravel of a certain size)


I thought about:


burning the particles, but that seems wasteful in terms of energy and requires some equipment (burner, fire proof permeable net, etc.)


I'm looking for a solution for some kg of 1mm to 3mm gravel in a 100 l aquarium filled with drinking water with a PH value of 7.2 to 8.

In case it's necessary to have more exact info what the particles in the gravel consist of, I'll ask a separate question how I can figure this out.
It's easier to use flotation or froth flotation to separate out the less-dense peat (silt?) and carbon (I assume from the activated-carbon filter) than to use a chemical reaction..

Simple flotation would depend on making a dense solution (e.g. saturated Epsom salt, $\ce{MgSO4}$) and shaking the gravel mix in it... if the liquid's density is greater than the average density of silt with its entrained air, the gravel will sink and silt float, to be skimmed off. You can reuse the liquid for more separation.

Froth flotation relies on a surfactant wetting the silt and keeping it suspended while the gravel settles out. Try a bit of hand dish-washing
detergent.