Nitrogen Cycle Investigation



Class Periods




Subject Areas



Students examine nitrogen test strip packaging, and practice measuring the ammonia, nitrite, and nitrate in various water samples.  This lesson should be followed by regular monitoring of the ammonia, nitrite, and nitrate level in the classroom tank.


  • Use and interpret water quality test strips.

Materials and Resources

Teacher Resources


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

  • Samples of different waters to test for ammonia, nitrites, and nitrates, such as:

    1. Harbor water

    2. Fish tank water

    3. Tap water

    4. Tap water in which you have dissolved varying amounts of plant fertilizer

    5. Toilet water

    6. Aged urine diluted in tap water

    7. Pond water

    8. Puddle water

    9. Rain water

    10. Tap water with a small amount of an ammonia-containing household cleaning product dissolved in it

    11. Tap water with a small amount of ammonium chloride salt dissolved in it

Before you get started


  • Decide in advance how you want to challenge your students while they practice testing water for ammonia, nitrates, and nitrites.  Prepare your samples and instructions accordingly.  Some options include:
    • You can label your water samples, and require students to predict which ones will have the most and least ammonia, nitrite, and nitrate before they start measuring.  This works best if they have some background in the subject, so they can make predictions that make sense to them.

    • You can not label your water samples, but give students a list of the possibilities.  (You can throw in some possibilities that aren’t actually there, too).  Then students can use their data to try to figure out which sample is what.

    • Students can create their own water samples to test, based on a prompt such as, “Prepare ten samples that show a range of levels of ammonia.  Let me know what materials you’d like to use, and I’ll see what I can find for you.”
  • Also decide in advance if you want to make your own version of the Handout Test Strips for Ammonia, Nitrites, and Nitrates -- using text from the actual test strip bottles that you have.

Instruction Plan


  1. Project the resource Tilapia in Tanks.  

  2. Students describe, respond to, interpret, and raise questions about the slides (see below).

  3. Explain: All tank animals -- including oysters! -- can be poisoned by their own waste turning into toxic ammonia and nitrites.  Both ammonia and nitrites are compounds of nitrogen.  Our goal is to figure out how to avoid this problem!  One thing we need is a way to monitor the nitrogen changes in our tanks.

    Compared with other fish, tilapia are pretty tolerant to changes in ammonia and nitrites.  So people often choose tilapia for aquaculture or aquaponics.

    From: http://blogqpot.com/images/minneapolis%20aquaponics

    But this can be the result of a nitrite spike during startup:


    From: https://www.friendlyaquaponics.com/2015/08/10/1833/


  1. Students explore the labels on the nitrogen test strips: it works best if you can take a good pictures of your own test strip container, and/or retype the text from it for all the students to read.

    • Alternatively, you can use the Handout Test Strips for Ammonia, Nitrites, and Nitrates, but it may not be identical to the kit you have.

    • Even better, recruit a local aquarium hobbyist or professional to visit your class and bring a bunch of test strip bottles to explore together!

    • Better still, take the class to visit the aquarium hobbyist or professional and their aquaria!

  2. If your students are already aware of water conditioning drops and/or a live bacterial culture additive such as StressZyme, you may decide to introduce the Handout Aquarium Additives- Water Conditioner and StressZyme at the same time.


As a whole class, students debrief their study of the packaging on their nitrogen test strips by sharing their questions, confusion, and insights. As they talk, post points of disagreement, shared understandings, and persistent questions.


In groups, students practice testing water for ammonia, nitrites, and nitrates.  Remember, as described in the “Preparation” section above, there are several ways to make this interesting, such as:

  • You can label your water samples,

  • You can not label your water samples,

  • Students can create their own water samples to test, based on a prompt


Students debrief in a full-class discussion.  As they talk, add to your posting of points of disagreement, shared understandings, and persistent questions.


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.