30L Aquaponic System

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Part 1: Quick Concepts

1. Which water temperature range is generally best for warm-water aquaponic fish (e.g. tilapia)?

18–22 °C

22–28 °C

28–34 °C

2. Check all factors that increase dissolved oxygen (DO) in a tank:

Surface agitation (waves/splashing)

Higher water temperature

Increased aeration (air stones, pumps)

Reduced stocking density

3. Typical recommended turnover rate for a small aquaponic tank (how many times tank volume passes through biofilter per hour):

0.5–1× per hour

2–6× per hour

10–15× per hour

4. Which benefits do plants provide in an aquaponic system? (check all that apply)

Uptake of dissolved nutrients (reduces nitrate/phosphate)

Produce oxygen through photosynthesis (daytime)

Create ammonia from fish waste

Provide surface area for beneficial microbes

Part 2: Formulas & Calculations (30 L system)

5. Fish stocking density — use the general formula and calculate for a 30 L tank.

Formula: Biomass_max (kg) = Volume_L × C (kg/L). Recommended conservative C = 0.01–0.02 kg/L (10–20 kg/m³).

a) Using C = 0.01 kg/L, Work out the Biomass_max for a 30 L system:

b) If average fish mass = 6 g (0.006 kg), how many fish can you safely keep in a 30 L system? (Number = Biomass_max / avg_fish_mass_kg)

6. System flow rate (pump sizing) — choose a turnover and calculate required flow.

Formula: (Litres/min) = (turnovers_per_hour × Volume_L) / 60mins

Using a turnover of 3× per hour, work out the Litres/min for 30 L:

7. Surface agitation index — check if your flow gives good surface renewal.

Formula: Surface agitation index SI = Q (L/min) ÷ surface_area_m². Aim for SI ≈ 10–50 L/min/m² depending on tank and fish load.

a) Measure or estimate your tank surface area (length × width in metres). Surface area = ______ m²

b) Using Q from Q6, calculate SI and state if it lies in the recommended range:

8. Presence of plants / growbed sizing — calculate a starting growbed area.

Formula: Growbed_area (m²) = Biomass_kg × G. Typical G for media beds ≈ 0.5–1.0 m² per kg fish (use 0.5 m²/kg for a conservative start).

Using Biomass_max from Q5, calculate growbed area (m²):

9. Atmospheric pressure effect on oxygen saturation — estimate DO change.

Formula (simplified): DO_new ≈ DO_standard(T) × (P_new_kPa ÷ 101.325)

If standard DO at your temperature is DO_standard and local pressure drops to 98 kPa, what fraction of DO_standard is available? (Compute 98 ÷ 101.325 and state percent.)

10. Short reflection: List three practical optimisation steps you would implement for this 30 L system (consider temperature control, stocking, flow, agitation, plants, aeration).