Billion Oyster Project

How Not to Kill your Animals with Ammonia and Nitrites


Nitrogen Cycle Investigation



Class Periods




Subject Areas



Students compare and evaluate the advice of several sources on how to protect their tank animals from ammonia or nitrite poisoning.  Based on that analysis, students collectively decide how they want to ‘cycle’ the classroom tank, and make predictions about the tank’s nitrogen and animal welfare in the weeks and months to come.  

As an extension, students can aim to create the best possible conditions for developing a community of nitrifying bacteria in smaller containers such as spice jars.  Later, if they can persuade their classmates that they have succeeded, the class may decide to incorporate some jars + contents into the classroom tank.

This lesson should be followed by daily monitoring of the ammonia, nitrite, and nitrate level in the classroom tank.  


  • Evaluate different approaches to ‘cycling’ an aquarium.

  • Predict ammonia, nitrite, and nitrate levels in the classroom tank in the coming weeks.

Materials and Resources


  • Everything you need for an oyster tank (see BOP Supply List or BOP Oyster Tank Guide)

  • Test strips for ammonia, nitrites, and nitrates  (see BOP Supply List)

  • Optional: a couple of ‘hardy’ animals to produce ammonia in your tank, such as mud crabs, mud snails, or possibly oysters

  • Molecular models of ammonia/ammonium, nitrite, nitrate, nitrogen gas -- one set for each group.  Note: students build their own models in a previous lesson, Get to Know a Few Nitrogen Molecules.

  • Optional, for “Extend” section of lesson: enough spice jars with lids (or similar container) for every group (or every student) to have at least one, plus enough extra tank supplies for students to mess around with creating optimal conditions for the growth of communities of nitrifying bacteria in their jar.  They’ll also need extra test strips to see if their plan is working.

Before you get started

Tips for Teachers

This lesson should be followed by daily monitoring of the ammonia, nitrite, and nitrate level in the classroom tank.  All the students need to be able to see the results of this monitoring daily.


Optional: Be ready to distribute and update students’ predictions from a previous lesson -- Oyster Tank Questions Part 3 - Will Our Oysters Do Better in the ORS or in the Classroom Tank? -- about whether their oysters will do better in the Oyster Restoration Station (ORS) or in the classroom tank.

Instruction Plan


  1. Students get their molecular models of ammonia/ammonium, nitrite, nitrate, and nitrogen gas, since they will need them later.

  2. Ask your students: “So far we know we can kill our tank animals with too much ammonia or nitrite.  What other questions do we need to try to answer, in order to do a good job of protecting our animals from ammonia or nitrite toxicity?

  3. Post students’ questions.


  1. Students get How to Regulate Nitrogen in Your Tank,

  2. With access to their nitrogen models, students skim the text looking for the names of the molecules.  

  3. If they like, they can place the appropriate model on the paper where the molecule is mentioned.


  1. In pairs, students choose one text from How to Regulate Nitrogen in Your Tank and complete Different Approaches to Regulating Nitrogen in Your Tank.  
    Note: this handout helps students organize advice from their selected text into a table, with columns for “Questions (about how to regulate nitrogen in your tank),” “Advice,” “Pros of the Advice,” and “Cons of the Advice.”  The “Questions” column contains eight questions that at least one of the texts offers advice on.  Teachers should feel free to edit the handout to reduce, add to, or rearrange the questions as they see fit.

  2. Fast-working pairs choose another text and get another copy of the worksheet.  This gives you a lot of flexibility to allow slow-working pairs enough time to digest at least one text thoroughly, to push fast-working pairs to go deeper, and to introduce more information to the class discussion later.


In pairs, or perhaps in pairs of pairs, students complete Your Recommendations for Regulating Nitrogen in Your Tank.


  1. In an extended class discussion, based on the information they have pulled together from their readings, students make the collective decisions:

    • Should we initiate a ‘fishless’ or animal-less nitrogen cycle in our tank?  Why or why not?

    • If we do add animals right away, how many and what kind?  Assuming we go to the ORS and find some animals, how shall we decide which ones to bring back?  What else will we need to know about our animals?  

    • What should we plan to do if our tank ends up with more ammonia or nitrite than is healthy for our animals?

    • Optional: If we don’t add animals right away, should we feed our ammonia-eating bacteria with ammonium chloride, a commercial cleaning product, a piece of fish or shrimp meat, a bit of fish food, nothing, or something else?

  2. Students predict how the ammonia, nitrite, and nitrate levels will change in the tank by tomorrow, in one week, and in one month.

  1. Class agrees to a regular monitoring and data-sharing protocol for ammonia, nitrites, nitrates, and pH.  

    (Students may not yet understand why it’s important to monitor the pH.  If you prefer, you could monitor the pH for them, at lest until they learn more about it.)

  2. Ask the students:

    • Based on what you’ve learned so far about nitrogen, do you think your oysters will do better in the tank or in the ORS?

      Post (changes to) their predictions.

    • What new questions do you have?

      Post their new questions.

Note:  Based on students’ decisions and predictions, schedule the appropriate timing for Is Our Tank Ready for (More) Animals?, an upcoming lesson in which the class examines the accumulated daily ammonia, nitrite, and nitrate data from the tank, and decides collectively whether the tank seems to be ready for animals.


  1. Each student or each group gets their own small containers (e.g. spice jars).  

    • Their task:  to create the best possible conditions for encouraging the growth of a community of nitrifying bacteria (the ones that transform ammonia into nitrites and nitrites into nitrates.

    • Their constraint: they need to do so in a way that will not stress or kill animals with excessive ammonia or nitrites.

    • They also have to figure out how to check if their approach is working.  

    • One issue to consider in advance: this requires some extra materials, and especially a lot of extra test strips.

  1. Later, their jars and/or the contents can be added to the classroom tank, if the students can make a good case to their classmates that they will be contributing a productive community of nitrifying bacteria.


NGSS - Cross-Cutting Concepts

  • Energy and Matter

    • Matter is conserved because atoms are conserved in physical and chemical processes.

NGSS - Disciplinary Core Ideas

  • ESS2.A: Earth’s Materials and Systems

    • All Earth processes are the result of energy flowing and matter cycling within and among the planet’s systems. This energy is derived from the sun and Earth’s hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth’s materials and living organisms.
  • LS2.B: Cycle of Matter and Energy Transfer in Ecosystems

    • Food webs are models that demonstrate how matter and energy is transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. Transfers of matter into and out of the physical environment occur at every level. Decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments. The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem.

NYC Science Scope & Sequence - Units

  • Grade 6, Unit 4

    • Interdependence

NYS Science Standards - Major Understandings

    • Matter is transferred from one organism to another and between organisms and their physical environment. Water, nitrogen, carbon dioxide, and oxygen are examples of substances cycled between the living and nonliving environment.