Aquarium Substrate, Gravel, Pebbles Sand;
Aquarium Gravel/Sand Substrate, Which to Use; Including Pictures. BASICS: For the average fish only freshwater aquarium I recommend 23" of #3 gravel (#3 gravel is .2 to .5 cm in size) or a larger pea sized gravel #5. (#5 is generally about 1 cm) This allows less build up of hydrogen sulfide producing anaerobic bacteria than with sand. The