Grow It: Aquaponics and Sustainable Systems

You need: A3 paper · coloured pens · three everyday systems: a toaster, the school canteen, a stream

1. Draw three boxes in a row: input, process, output.
2. For a toaster: bread and electricity in, heating out, toast and heat out.
3. Do the same for the canteen and a stream.
4. Draw a feedback arrow from output back to input where one exists (a thermostat, a customer complaint, rain).
5. Circle any subsystem: a smaller system inside the big one.

How you'll know: You can draw any system as input → process → output and point out its feedback loop.

Go further: Draw your own body as a system. What are the inputs, outputs and feedback loops?

You need: aquarium test kit or strips (pH, ammonia, nitrite, nitrate) · thermometer · clean cups of tap, rain and pond or tank water · gloves and goggles

1. Label each cup and measure the temperature.
2. Follow the test-kit steps exactly for pH, ammonia and nitrate.
3. Match the colours on the chart in good light and record the numbers.
4. Compare with safe ranges: pH around 6.8 to 7.2 in aquaponics, ammonia and nitrite as close to zero as possible.

How you'll know: Your table shows each water sample's results and you can say which is safest for fish.

Safety: Gloves and goggles; don't taste, smell closely or pour test chemicals down your hands; wash hands afterwards; teacher disposes of test liquids.

Go further: Test the same water at the same time each day for a week and look for patterns.

You need: role cards: fish, ammonia, bacteria A, nitrite, bacteria B, nitrate, plant · coloured bibs or string · open space

1. Fish 'breathe out' ammonia: hand an ammonia card to the next person.
2. Bacteria A swap ammonia for nitrite; bacteria B swap nitrite for nitrate.
3. Plants collect nitrate and 'grow' (step forward).
4. Now remove bacteria B. What piles up? What happens to the fish?
5. Try again with too many fish, or too few plants.

How you'll know: You can explain why bacteria are the most important living thing in the system, even though you can't see them.

Go further: Draw the cycle as a diagram with arrows and explain where it could break.

You need: a recycled food-grade barrel, crate or large tub · plastic liner if needed · a length of slotted drainage pipe and a vertical fill pipe · gravel or scoria · weed mat or shade cloth · compost-rich soil · seedlings

1. Drill an overflow hole in the side about 25 to 30 cm up from the base (adult).
2. Lay the slotted pipe along the bottom and connect the vertical fill pipe so it sticks up above the soil.
3. Fill with gravel up to the overflow hole: this is the water reservoir.
4. Cover with weed mat, then fill with soil and plant seedlings.
5. Fill through the pipe until water runs out of the overflow. Record how much water it took.

How you'll know: The reservoir fills from the bottom and the soil stays damp without top watering.

Safety: Adults drill and cut; gloves for gravel; check the barrel only held food-safe contents; lift heavy bags in pairs.

Go further: Record how many days until you need to refill, and compare with a normal pot.

You need: tank of 40 to 100 litres with established bacteria · small submersible pump and tubing · grow bed or tray with drain holes · rinsed expanded clay balls · lettuce, pak choy or basil seedlings · RCD-protected power outlet · goldfish (added by the teacher when the system is cycled)

1. Set the tank on a strong, level bench; water is heavy (1 litre weighs 1 kg).
2. Rinse the clay balls until the water runs clear, then fill the grow bed.
3. Place the grow bed over the tank so it drains back into it.
4. Fit the pump and tubing; an adult makes drip loops in the cable and plugs it in.
5. Plant seedlings, wash their roots gently and record their height.

How you'll know: Water flows from tank to grow bed and back without leaks, and every subsystem is labelled on your diagram.

Safety: Only adults handle plugs and pumps; hands out of the water while the pump is on; mop spills immediately; follow the class animal-care plan.

Go further: Time the fill and drain cycle and work out how many times a day all the tank water passes through the plants.

You need: shared spreadsheet · test kit · thermometer · ruler

1. Every school day, record temperature, pH, water added, feed given, plant height and fish behaviour.
2. Twice a week, add ammonia, nitrite and nitrate.
3. Make line graphs with the date along the bottom.
4. Mark anything unusual (cold night, extra feeding, power cut) on the graph.

How you'll know: You can point to a change on your graph and explain what caused it.

Go further: Add a micro:bit to log water temperature every hour and compare day and night.

You need: your system or wicking bed · an ordinary pot or bed with the same plants (control) · measuring jug · log sheet

1. Record every litre added to each system for two weeks.
2. Water the control pot only when the top 2 cm of soil is dry.
3. Measure the tallest leaf of each plant at the start and end.
4. Work out litres used per centimetre of growth for each system.

How you'll know: You have a fair comparison of water use and growth, with the same plants and the same light.

Go further: Scale it up: how much water could the school garden save over a summer?

You need: scenario cards (power cut, holiday, heat wave, overfeeding, a helper adds vinegar) · system diagram · timer

1. Draw a card. Predict what happens in the first hour, first day and first week.
2. Trace the effect around your system diagram: which subsystem fails first?
3. Design a response and a prevention for each scenario.
4. Add the best ones to the care guide's 'what to do if…' page.

How you'll know: Every risk in your care guide has a warning sign, a response and a prevention.

Go further: Work out the pump's yearly energy use and cost, then design a version that needs no power.