Impregnated Gravel?

Hi,

I am hoping somebody on this group may be able to point me in the right
direction.

I am doing a high school research project that involves keeping
some fish (specifically, Siamese Fighting Fish). The one that I bought
comes in a small plastic container, with some apparently "special" gravel
at the bottom of the tank that I gather is somehow impregnated with
nitrifying bacteria.

Now my question is about the gravel (I need to discuss an innovation for
my research report). Has anyone heard of such bacteria-impregnated gravel?
Where can I look to find out more about it, such as who invented it and
when, how is it made, and what its properties, advantages and
disadvantages are? I asked the people who sold me the fish and they were
strangely evasive -- presumably because they don't want anyone cutting in
on their business.

I would be very grateful for any clues, no matter how small.

Thank you very much.

Regards,

Emily