Billion Oyster Project

Create Brackish Water for Your Oyster Tank


Oyster Tank Investigation



Class Periods




Subject Areas

Science, Math


Students work together to create brackish water with the correct salinity for their tank.


    • Experiment through trial and error.
    • Calculate correct salinity for the oyster tank water.
    • Analyze the process for getting to the correct salinity.

    Materials and Resources

    Student Handouts


    • Classroom oyster tank (at least 5 gallons)
    • Instant Ocean Sea Salt
    • 10 one-gallon containers
    • 10 hydrometers
    • Variety of measuring cups, spoons, etc.

    Before you get started


    One-gallon Containers:
    • For the one-gallon containers needed for this lesson, we recommend Lee's Kritter Keeper, Small, because this size tank is useful for other BOP lessons and units.
    • You could also use small buckets or one-gallon milk jugs with the top cut off.
    • Whatever you choose, just make sure there is enough room in the container to add a gallon of water and stir in the salt.

    Instruction Plan


      1. In this activity, students will prepare the salinity mixture for the tank.

      2. Each group gets a one-gallon container.
        • Note: You may want to pre-fill the containers with water or you may want to have the students fill up their own containers.

      3. Each groups gets 1 cup of Instant Ocean Sea Salt.

      4. Explain: You want the salinity of your classroom tank to be approximately 15ppt (parts per thousand).

      5. Note: The easiest way to get to 15ppt is through trial and error.  If you want to challenge the students mathematically, consider giving them the following information:
        • 1 cup of Instant Ocean mixed in 1 gallon of water = 1.023 sg (specific gravity) = 30-35ppt

      6. Students are provided with a variety of measuring cups, spoons and tools to choose from.  

      7. Let the students experiment and work out how to get to 15ppt!
        • Note: You may want to advise students that they should start with a small amount of Instant Ocean and then use the hydrometer to measure the salinity.  It is easier to incrementally add more Instant Ocean to get to 15ppt than to add too much and try to bring the salinity down.

      8. Consider gathering the students’ trial and error results and posting them so students can look for a pattern within the results and alter their experimentation accordingly.  If students are using different tools (e.g. cups, teaspoons, etc.), you may want to standardize the results that are posted (for example grams of salt instead of cups and tablespoons.  This will make it easier to see a pattern.


      Salt (grams)

      Water (mL)

      Salinity (ppt)











      1. When they are ready, check each group's salinity.

      2. Once all groups have the correct salinity, each group pours their gallon of brackish water into the classroom oyster tank.  

        • Consider making this into a bit of ceremony, as students embark on taking care of their oysters!

      3. Discuss the process of getting the correct salinity.  

        • Questions: How did it go?  What did they notice?  What questions came up?  What surprised them?  

        • Take notes on your students’ thinking!  These notes are extremely useful later in the year, and there is no way to re-create them later!

      4. Each student gets an Oyster Tank Analysis worksheet and completes the “Mixing the Salt Water” section.


      NYC Science Scope & Sequence - Units

      • Grade 6, Unit 4

        • Interdependence
      • Grade 7, Unit 4

        • Dynamic Equilibrium: Other Organisms