SANITATION (cont)
Gravel or other types of substrates are often used for biofiltration. Biofiltration is accomplished by moving water over these materials that contain naturally occurring bacteria. Some of the bacteria then convert ammonia to nitrite and another group of bacteria then converts nitrites into nitrates. Since nitrates are stable they are usually removed by changing water on a regular basis.
A siphon can be used to remove fecal material from the bottom of a tank while simultaneously replacing some of the water in the tank.
Siphon for removing fecal material