Last Updated on November 5, 2024 by Sara Rose
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Aquaponics Grow Bed Calculators: A Guide to Ratios and System Setup
In aquaponics, determining the right grow bed area and fish tank volume is crucial for system success. The grow bed calculator helps balance the nutrient input from the aquaculture (fish) system with the nutrient uptake by the plants. The correct ratio ensures both your fish and plants thrive while minimizing waste and nutrient imbalances.
There are two primary approaches to calculating these ratios: Dr. Rakocy’s Method (ideal for small-scale/hobbyist systems) and Dr. Lennard’s Method (better for commercial-scale systems). Both methods are scientifically based and ensure that nutrient needs are met for healthy, productive aquaponic setups.
Understanding Aquaponics Ratios
Aquaponics combines two distinct practices—aquaculture (raising fish) and hydroponics (growing plants in water)—which makes it more complex than it initially appears. Both fields require in-depth research and hands-on experience to design a successful system.
- Fish Stocking Density: The number of fish in the system, directly affecting nutrient input.
- Plant Species: Different plants have different nutrient requirements, influencing the amount of feed needed.
- Feed Conversion: The amount of fish feed required daily, which drives nutrient levels in the system.
By calculating the correct fish-to-plant ratio, you ensure optimal nutrient flow from the fish to the plants, while also avoiding excess nutrients that could harm the system.
Key Considerations for Aquaponics Grow Bed Calculations
Before you calculate the required grow bed area and fish tank size, you should consider these important variables:
- Purpose of the System: Is it a small hobbyist setup or a large commercial operation?
- Plant Species: Select plant species and calculate their nutrient requirements.
- Fish Feed: Estimate how much fish feed will be provided daily.
- Fish Biomass: Calculate how many fish are needed to supply nutrients for the plants.
- Stocking Density: Determine the number of fish per gallon of tank water.
- System Volume: Determine how many gallons of water your fish tank should hold.
- Grow Bed Area: Determine how much grow bed area will be needed to support the plants.
Dr. Rakocy’s Method (For Small-Scale or Hobbyist Systems)
Dr. Rakocy’s method calculates nutrient requirements based on the total daily fish feed and plant area. It’s particularly useful for backyard or small-scale systems, such as home gardens or hobbyist setups.
Fish Feed and Grow Bed Calculation Table (Rakocy’s Method)
| Plant Type | Feeding Rate (oz per sqyd/day) | Grow Bed Area Needed (sq ft) | Fish Stocking Density (Fish per gallon) | Fish Tank Volume (gallons) |
|---|---|---|---|---|
| Leafy Greens (e.g., Lettuce) | 2 oz per sq yd/day | 1-2 sq ft per plant | 1-2 fish per gallon | 10-15 gallons per 10 plants |
| Fruiting Plants (e.g., Tomatoes) | 3 oz per sq yd/day | 1-1.5 sq ft per plant | 1-2 fish per gallon | 15-20 gallons per 10 plants |
Example Calculation Using Rakocy’s Method (Hobbyist)
Assume you have 50 fish (1 fish per gallon) and plan to grow 50 leafy greens (e.g., lettuce) in a raft system.
- Fish Feed: If you feed 2 oz per fish per day, total feed = 50 fish × 2 oz = 100 oz/day.
- Grow Bed Area: For leafy greens, the recommended feeding rate is 2 oz per square yard/day.
- Total square yards needed = 100 oz ÷ 2 oz per sq yd/day = 50 square yards.
- Convert to square feet: 50 square yards × 9 sq ft per sq yard = 450 sq ft of grow bed area.
- Fish Tank Size: With 50 fish, you’ll need a 50-gallon fish tank.
Dr. Lennard’s Method (For Commercial Systems)
Dr. Lennard’s approach is more specific and scientifically balanced for commercial-scale systems. It focuses on matching the nitrogen requirements of plants with the nutrients available from the fish feed. Dr. Lennard has summarized this ratio into a calculator which includes the required biofilter for nitrogen fixation on his website.
Fish Feed and Grow Bed Calculation Table (Lennard’s Method)
| Plant Type | Plant Nitrogen Requirement (g/day) | Fish Feed (g/day) | Fish Stocking Density (Fish per gallon) | Fish Tank Volume (gallons) | Grow Bed Area (sq ft) |
|---|---|---|---|---|---|
| Leafy Greens | 1-2 g/day per plant | 10-20 g/day per plant | 1-2 fish per gallon | 10-15 gallons per 10 plants | 20-30 sq ft (for 100 plants) |
| Fruiting Plants | 5-7 g/day per plant | 50-70 g/day per plant | 1-2 fish per gallon | 30-40 gallons per 10 plants | 40-50 sq ft (for 100 plants) |
Example Calculation Using Lennard’s Method (Commercial)
Assume you have 200 fish (stocked at 1.5 fish per gallon) and plan to grow 100 fruiting plants (e.g., tomatoes).
- Fish Feed: If each fish requires 3 oz of feed per day, total feed = 200 fish × 3 oz = 600 oz/day.
- Plant Nitrogen Needs: Each tomato plant requires 6 grams of nitrogen per day. For 100 plants:
- Total nitrogen needed = 100 plants × 6 grams = 600 grams of nitrogen per day.
- Fish Tank Volume: Based on 600 grams of nitrogen from the feed, you’ll need approximately 200-250 gallons of water for 200 fish.
- Grow Bed Area: With 600 grams of nitrogen available, you’ll need about 500-600 sq ft of grow bed area for 100 fruiting plants.
Conclusion
Whether you’re designing a small-scale hobby system or a large commercial aquaponics operation, understanding the relationship between fish feed, plant needs, and grow bed area is essential for system success.
- Dr. Rakocy’s Method works well for small systems, focusing on the total feed input and general nutrient availability per square yard.
- Dr. Lennard’s Method is ideal for larger, commercial systems, offering a more precise calculation that balances nitrogen requirements and feed input for optimal plant growth.
By using these calculators and methods, you can set up an aquaponics system that meets the specific needs of both your fish and plants, ensuring a healthy and productive setup.
Learn more about: How Many Fish Can You Put In A 5 Gallon Tank
From the information defined in these steps, you will be able to choose between the practices of Dr. Rakocy or Dr. Lennard. I only follow Dr. Lennard’s practice since most of the systems I design are aimed toward commercial production. Dr. Rakocy’s system works well with backyard and hobbyist-scale aquaponics which use different plant species.
Read more about:Aquaponics Growing Medium
