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ACTIVITY EXTENSION: Hydroponics to Aquaponics

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

Below are some modifications to convert hydroponic into an aquaponics system. This can be done in a series of lessons and activities to build understanding of NGSS grade 5 performance expectations:

5-LS1-1: Support an argument that plants get the materials they need for growth chiefly from air and water.

and

5-LS2-1: Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment

The activity below draws from the content in the page Materials for Plant Growth and Ecosystem Cycling and is modified from the activities: Build a Hydroponic System and Aquaponics in a Bottle.

Phenomenon:

<p>Fig. 1. Waterfalls in Hawai'i help to cycle matter as part of a bigger ecosystem.</p>Materials cycle through an ecosystem that allows the plants and animals to survive and grow (Fig. 1). 

Inquiry:

Can plants survive and thrive without soil? How does matter cycle through the ecosystem?

Guiding Questions:

  1. Where to plants get the energy needed to survive?
  2. Where do animals get the energy they need to survive?
  3. What happens to the materials that animals eat?

Activity:

Build your own hydroponic system that can be converted into aquaponics! 

Note: Hydroponics is the method of growing plants in water (without soil). In comparison, Aquaponics is a system that combines aquaculture (the growing of aquatic animals, like fish, snails, clams, etc.) in combination with hydroponically grown plants.

Materials:

Hydroponics

  • <p>Fig. 2. The three main supplies needed to start building a hydroponics system are the tank, basket, and plant!</p>Tank for water (or other clear, large container)
  • Plastic basket for plant (or other container that can fit inside the tank. This basket should have holes so water can circulate the roots of the plant) (Fig. 2)
  • Wooden dowel (x2 that are long enough to span more than width of the tank)
  • Substrate for inside the tank (e.g. Sand (washed), Fish tank rocks)
  • <p>Fig. 3. Black cinder works well as a root structural support for a hydroponic or aquaponic system.</p>Root structural support (e.g. cinder (Fig. 3), gravel, wood fibers, perlite, vermiculite, pumice or grow stones)
  • Larger rocks for tank adornment
  • Small plant for hydroponic growth (herbs like basil grow easily and quickly)
  • Small plant in larger pot for growth in soil (herbs like basil grow easily and quickly)
  • Aerator and airstones
  • Nutrients (e.g. nutrient additive such as MiracleGro. Tomato plant food generally has the right proportions of nutrients and will do the trick).
  • Optional (but very helpful!): Magnetic glass cleaner to remove algae
  • Optional: pH test kit
  • Ruler

Aquaponics additions

  • Guppies, snails, and/or shrimp
  • Aquatic plant
  • Optional (but very helpful): filter (can be purchased online or at local pet shop)

Teacher Recommendations:

  • If possible, take students on a field trip to collect organisms like small fishes, snails, and aquatic plants from nearby streams. If you cannot collect enough organisms for the entire class, you can purchase small fishes and aquatic plants from a pet store.
  • Allow the water to sit out for at least 24 hours so the chlorine in the tap water evaporates (or use commercially available drops to treat the water).
  • Pre-rinse the gravel so that there is no mud or sand.  You will need enough gravel to fill the bottom of the bottles and hold the Elodea plants in place.
  • You can build one larger system for the whole class, or have multiple systems with smaller tank/basket combinations. 
  • You may want to pre-drill the holes in the baskets so students only have to assemble it. 

Important Note to the Teacher:

Invasive species concerns: It is important to dispose of organisms (plants, fish, snails, etc) properly so that native habitats are not harmed. Return organisms to the place wher you caught them, but do not release organisms bought from the pet store into the natural environment. The release of pet store guppies is likely the reason for their presence in Hawaiian streams and their negative impact on native species: See DLNR page on guppies for more info.

Please see http://www.habitattitude.net/ for guidance on aquarium disposal.

Care of living organisms: This activity involves observation and experimentation with small fish, which are vertebrates. Consideration of proper, humane care of vertebrates is important.  Provide explicit guidance for students to develop an understanding of and value for life and living organisms. The guppies must be provided with appropriate daily care so that they remain healthy during the course of the experiment and should not be subjected to pain or discomfort.

Students need to be supervised by a teacher that understands the safe and responsible use of animals in the classroom and who understands and follows Hawai‘i Department of Education policies and other relevant regulations. Teachers must develop and implement a plan for the future care of the fish and other organisms following the study.
(Adapted from the National Science Teacher Association’s 2005 Position Paper: “Responsible Use of Live Animals and Dissection in the Science Classroom”)

Proper care of small fish, like guppies includes:
1. Feeding them daily, i.e. making sure there is a source of food such as elodea, or providing fish food flakes.
2. The temperature of the water must be between 72° and 82° F.,
3. Change approximately 1/3 of the water every 1 to 2 weeks, or as needed to keep the water in good condition.
4. Create a happy or natural environment by adding things like gravel and plants to the tank. Care of the guppies must be provided daily, including weekends, holidays, and other times school is not in session. When the experiment is over you must continue care of the guppies in the classroom or implement another plan for the continued proper care of the guppies, as they cannot be re-introduced into Hawai‘i’s environment.
For further information regarding current policies and regulations in Hawai‘i contact the Science Section of the Instructional Services Branch of the Office of Curriculum, Instruction, and Student Support at the Hawai‘i Department of Education. 

These recommendations can be viewed in the attached pdf below:

Build your Hydroponic System!

  1. Follow along on your worksheet to build and observe hydroponic plants and then turn your system into a thriving aquaponics tank!
  2. You will compare plants grown hydroponically to those grown in soil.
    Note: Hydroponics is the method of growing plants in water (without soil). In comparison, Aquaponics is a system that combines aquaculture (the growing of aquatic animals, like fish, snails, clams, etc.) in combination with hydroponically grown plants.
    1. To prepare, replant one of your small plants into a larger pot so that it has space to continue to grow in soil. 
  3. You will be measuring your plants' growth and recording your results in the data table on your worksheet. Choose a consistent method to measure, for example:
    1. Place the bottom of the ruler at the base of the plant and measure to the tip of the main stem.
    2. Count the number of leaves, or choose a leaf to measure each time.

Prepare your tank!

  1. Rinse the tank substrate with warm water a few times to prepare it for your ecosystem. Make sure the tank is clean as well!
  2. Find a location for your tank with direct access to sunlight and near an outlet (to plug in the aerator).
  3. Layer about an inch or two of the substrate on the bottom of the tank.
  4. <p>Fig. 4. The water in this newly established hydroponic system is settling.</p>Fill the tank with water. The water may look cloudy at first while the substrate settles (Fig. 4).
  5. Place the airstone on the bottom of the tank and plug in the aerator. You can bury it slightly under the substrate.
  6. Add nutrients according the the instructions on the packaging and based on the size of your tank.
  7. Place your plant growing in soil (from #2) next to the tank so it has access to sunlight. Allow it to grow here for the remainder of the study.
  8. Measure the starting height of your soil plant and record it on your worksheet.

Prepare your plants!

  1. With help from your teacher, drill two holes on each side that line up with two holes on the other side of the basket. 
    Note: the holes should be big enough for the wooden dowel to slide through. The holes should also be positioned so that 2/3 of the basket falls below the top of the tank. This will ensure your plant roots will be able to reach the water.
  2. Push the dowels all the way through the holes so that they stick out on either side.
  3. Fill the basket halfway with your chosen root structural support (e.g. cinder).
  4. Remove your plant from the pot and gently brush the soil away from the root structures.
  5. Hold the plant in place in the basket and fill in the remaining space with more support material so the plants are stable.
  6. Place the basket with your newly secured plants on top of the tank so that the wooden dowls rest on the tank edges (Fig. 3). 
  7. If the water is not touching the basket, add more until it does (Fig. 5). 
  8. Measure the starting height of your hydroponic plant and record it on your worksheet.

Explore hydroponic growth!

  1. Now that your hydroponic system is set up, maintain the system and observe plant growth!
    1. Water will evaporate over time, so you will need to refill your container. Every time (or every other time!) that you refill, add more nutrients to keep the plants growing well.
  2. Optional: Use your pH test kit to check the pH regularly. This will help ensure your system is stable. Basil likes a pH of about 6.5-6.8, so you can adjust as needed using your pH up or down bottles in the test kit.
    Note: If you are making your own nutrient solution rather than using plant food, review Perfecting the pH of your Hydroponic Nutrient Solution.
  3. <p>Fig. 5. This tank has been used to grow plants hydroponically but can be converted into aquaponics by adding organisms!</p>Continue monitoring and measuring your plant growth for your desired amount of time. When you are ready to convert your system into aquaponics, move on to the steps below (Fig. 5)!
  4. Compare these results to the plant grown in soil only.

 

Update your Hydroponics to Aquaponics

  1. Before you begin, answer these questions:
    1. How do scientists study plants and animals in their natural habitats?
    2. What might be some limitations, challenges, or risks with studies in the natural environment?
    3. What is the ethical treatment of living things? How will you ensure your animals are being treated ethically?
    4. Why do animals, including humans, eat things?
    5. Do plants eat?
    6. What is a producer? Consumer? Decomposer?
  2. Allow your hydroponics system to cycle out excess nutrients before adding fish - i.e. give the water some time since you last added nutrients. You may also want to change out 1/3 of the water a few days before adding organisms.
  3. Review the recommendations for managing care of living organisms (teacher recommendations box below materials list).
  4. Collect organisms from a local stream if you have permission and safe, easy access.
    1. Organisms may include guppies, snails, shrimp, and freshwater plants such as elodea and duckweed, etc.
      Note: If you don’t have access or permission to a local stream, organisms can be purchased from a pet shop.
  5. Add a few large rocks to the bottom of the tank. These will provide unique structure to the bottom that the fish can swim around. 
  6. Add the aquatic plants to your tank. Tuck the roots into the substrate. You may need to add a large rock nearby to hold the roots down.
  7. Gently add the fish and other organisms to the tank.

Care for your ecosystem!
Note: Your system should be able to maintain itself through the cycling of matter between producers, consumers and decomposers. However, since this system is small and might not represent every trophic level, you will still need to feed the fish to ensure they are getting enough energy (Fig. 6).

  1. <p>Fig. 6. This simple aquaponics system is successful at cycling material between plants and animals.</p>FEEDING: Drop a few flakes or pellets (depending on food choice) on the surface of the water to feed the fish few days (every 2 or 3 days should be fine).
  2. CLEANING: You will need to replace about 1/3 of the water every 1-2 weeks as needed. This will prevent algae buildup and ensure enough oxygen is available (The plants will contribute to the oxygen available).
    1. Prepare replacement water the day before, allowing it to sit out over night to evaporate any chlorine.
    2. Remove the top (plant or cap) and scoop out about 1/3 of the water using a cup (a turkey baster can also provide easy access to removing water). Be careful not to scoop any fish with the water!
    3. If there is algae build up on the exposed walls, you can wipe it off with a paper towel or clean sponge to prevent overgrowth.
      Pour in fresh water slowly so as not to stir up any loose particles. Alternatively, if you have a magnetic tank cleaner, use that to wipe the walls regularly to clear the algae.
  3. Optional: Monitor pH:
    1. If you keep up with changing the water the pH should stay relatively stable, however biological activity within the tank can cause the pH to fluctuate. Use your pH test kit to check the pH.
      Note: Review this helpful link on Aquarium pH for guidence.
    2. Additionally, a filter will help maintain the pH. Although the plant roots are doing some filtration, a filter may help to keep your system stable.

Activity Questions

Hydroponics Activity Questions:

  1. What happened to your best growing plant during the experiment?
  2. Where did your plant get its energy to grow?
  3. What resources did you give your plants?
  4. Compare the basil grown in soil versus the one grown hydroponically:
    1. How much did your hydroponic plant grow?
    2. How much did the plant in soil grow?
  5. Collect the class data for plant growth:
    1. What was the class average hydroponic plant growth height (inches)?
    2. What was the class average soil plant growth (inches)?
  6. How does your data compare to the class average?
  7. Did the plants need soil to grow? What evidence do you have?
  8. Why do you think plants normally grow in soil?
  9. What do you think soil provides to plants?
  10. How are hydroponic plants surviving without soil?
  11. Aquaponics is a system that combines aquaculture (the growing of aquatic animals, like fish, snails, clams, etc.) in combination with hydroponicly grown plants. In aquaponic systems, growers do not need to add nutrients (like you did in this hydroponic experiment). Explain why aquaponics systems do not need added nutrients.

Aquaponics Activity Questions:

  1. Match the vocabulary words with their definitions below. Then use the information to answer the activity questions.
Matter   An organism requiring food, which it gets by eating other organisms.
Consumer   An organism, often bacteria, fungus, or invertebrate, that breaks down waste from other organisms and converts it .
Decomposer   Organisms that use energy from the sun and matter in air and water to grow.
Primary Producer   Any substance that has mass and takes up space by having volume.
  1. What role does your plant play in making food from matter your ecosystem-in-a-bottle?
  2. What role does your fish/snail play in moving matter your ecosystem?
  3. What role does the bacteria living on the rocks play in recycling matter in your ecosystem?
  4. Which organism in your ecosystem is a:
    1. Primary producer?
    2. Consumer?
    3. Decomposer?
  5. How do the organisms in your ecosystem work together to recylce matter and produce food?
  6. Draw your own food web based on your ecosystem in a bottle (there are many correct food webs!). Label the primary producer, consumer, and decomposer.
  7. What might happen if a higher level predator was introduced to your ecosystem (such as a crayfish, large fish, or large frog)?
  8. Is there evidence of any other plant life in the aquarium? (Hint: It is possible that microscopic freshwater algae may have grown, and if it becomes dense enough may appear either as a greenish film, or perhaps a greenish hue in the water.)
  9. How are models beneficial to scientists when studying plants and animals?
  10. How could you improve your design for a future aquaponics system?

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.