Is gravel with 3 - 6 mm grain size suitable?
I want to set up a freshwater aquarium, can I use gravel with 3 - 6 mm grain size for this purpose?
This is not entirely optimal. Food and fish waste remainders easily sink between the relatively large "pebbles". As far as the food is concerned, it is not accessible for the fish any more, and both lead to the bottom ground becoming "sticky" more quickly. Furthermore, such coarse gravel is not quite suitable for fish that dig in the ground (e.g. Corydoras catfish, many loaches etc.).
I therefore recommend fine grained (< 2 mm) gravel or, even better, sand - in both cases round grained and without sharp edges!
Dr. Bodo Schnell