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Lessons 4: How Do Bacteria Affect the Nitrogen Cycle in an Aquarium?

Nitrogen occurs in three common substances found in an aquarium: ammonia, the nitrite ion, and the nitrate ion. Bacteria can affect the concentration of these substances in the tank. Which substance do they most directly impact?

Doing the science

  1. Start the Aquarium Sim.
  2. Select the "Fish" option on the left side menu bar. Choose a fish and click the "Add" button.
  3. Repeat step 2 to add a second fish to the tank.
  4. Select "Time Scale" from the left side menu bar. Adjust the time scale to "1 sec = 1 hour."
  5. Click on "View Status" on the left side menu bar and record the ammonia level. Then click the "Ok" button.
  6. Click on the "Bacteria" option on the left-side menu bar.
  7. Add 20 ppm of bacteria to the tank.
  8. Click on the "View Status" on the left side menu bar and record the new ammonia level.
  9. Repeat steps 5 – 8.

Do You Understand?

  1. How did adding bacteria affect the concentration of ammonia in the aquarium?


  2. What implications does the relationship you described in the previous question have on living organisms in the tank?