Lesson guide · Lesson 22 · Grades 4–8 · 7 min

When things go wrong: fish, plants, or bacteria?

Trouble in an aquaponics system can start with the fish, the plants, or the bacteria. A test kit helps you find which.

Open the lessonPrintable worksheet

Students will

  • Name the four things growers test in an aquaponics system: ammonia, nitrite, pH, and temperature.
  • Explain what a high ammonia or a high nitrite reading can mean.
  • Explain why growers change one thing at a time and then watch.

New words

test kit
A set of small tests that tell you what is in your water, like ammonia and pH.

Talk about it

When something goes wrong at home or at school, how do you find out what caused it?

Check questions and answers

  1. Fish gasp at the top of a system set up one week ago. What is wrong?

    • The crew isn't ready yet (answer) Right. A new system has few Munchers, so ammonia builds up.
    • The plants are too big Not quite. In a new system, the plants are still small. Think about the crew.
    • The water is too clean Not quite. Clear water can still hold ammonia. Test it to find out.

  2. The test kit shows high nitrite. What does that mean?

    • The Finishers are behind (answer) Right. Finishers change nitrite into nitrate. They can't keep up yet.
    • The plants need more light Not quite. Light doesn't change nitrite. Think about the crew.
    • The fish need more food Not quite. More food makes more waste. That would make it worse.

  3. Why do growers change only one thing at a time?

    • So they can tell what helped (answer) Right. Change one thing and watch. If it helps, you know why.
    • So the water stays the same color Not quite. Color isn't the point. Think about finding the cause.
    • Because tests only work once a week Not quite. You can test any day. Think about finding the cause.

Teacher note

This lesson needs no live fish. The Tank doctor cases are practice on screen. If a class keeps fish, follow the school's animal policy.

Sources

  • Somerville, C., Cohen, M., Pantanella, E., Stankus, A. and Lovatelli, A. Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fisheries and Aquaculture Technical Paper No. 589. Food and Agriculture Organization of the United Nations, Rome, 2014.
  • Deer, C., Hu, B., Dunn, B. and Dusci, J. Nitrification and Maintenance in Media Bed Aquaponics. Fact sheet HLA-6729. Oklahoma Cooperative Extension Service, Oklahoma State University, October 2021.
  • Mullins, C., Nerrie, B., and Sink, T. D. Principles of Small-Scale Aquaponics. SRAC Publication No. 5007. Southern Regional Aquaculture Center, September 2015.
  • Rakocy, J. E., Masser, M. P., and Losordo, T. M. Recirculating Aquaculture Tank Production Systems: Aquaponics, Integrating Fish and Plant Culture. SRAC Publication No. 454. Southern Regional Aquaculture Center; Oklahoma Cooperative Extension Service.
  • Chappell, J. A. Nitrite Poisoning or Brown Blood Disease: A Preventable Problem. Auburn University, 2008.
  • Francis-Floyd, R., Watson, C., Petty, D., and Pouder, D. B. Ammonia in Aquatic Systems. FA16. UF/IFAS Extension, University of Florida.
  • Paracueles, C. N. L. Toxicity of Ammonia on Oreochromis niloticus Fingerlings. Journal of Environment and Aquatic Resources, Mindanao State University at Naawan, 2015.
  • Sallenave, R. Understanding and Preventing Fish Kills in Your Pond. Guide W-105. New Mexico State University, College of Agricultural, Consumer and Environmental Sciences.
  • U.S. Geological Survey, Water Science School. Dissolved Oxygen and Water.