Aquaponics Fish-to-Plant Ratio Calculator
Calculate the ideal fish stocking density and plant bed size for a balanced aquaponics system.
Aquaponics combines fish farming (aquaculture) with soilless plant growing (hydroponics) in a symbiotic system. Fish waste provides nutrients for plants, and plants filter the water for fish. Getting the fish-to-plant ratio right is essential for a healthy, balanced system.
The Fundamental Ratio:
The most widely used guideline is the fish-to-grow-bed ratio:
1 lb of fish per 5–10 gallons of grow bed media
or equivalently:
1 kg of fish per 40–80 liters of grow bed media
Fish Stocking Density:
Maximum fish density = 1 lb per 5–10 gallons of fish tank water
or 1 kg per 40–80 liters
Beginners should start at the lower density (1 lb per 10 gallons) and increase as they gain experience and their biofilter matures.
Feed Rate Ratio (more precise method):
Daily fish feed (grams) = Grow bed volume (liters) × 0.5 to 1.0
Plant area (m²) = Daily feed (grams) / 60 to 100
This means for every 60–100 grams of fish food fed daily, you can support approximately 1 square meter (10.8 sq ft) of grow bed.
Common Aquaponics Fish Species:
| Fish | Water Temp | Growth Rate | Taste | Beginner Friendly |
|---|---|---|---|---|
| Tilapia | 75–86°F (24–30°C) | Fast (6–9 months) | Mild, excellent | Yes |
| Catfish | 75–85°F (24–29°C) | Fast (8–12 months) | Good | Yes |
| Trout | 50–65°F (10–18°C) | Moderate | Excellent | Moderate |
| Goldfish | 60–75°F (16–24°C) | Decorative only | Not edible | Yes |
| Koi | 60–78°F (16–26°C) | Decorative only | Not edible | Yes |
| Perch | 65–78°F (18–26°C) | Moderate | Good | Moderate |
Plant Capacity by System Size:
| Fish Tank | Grow Bed | Fish (at maturity) | Plants |
|---|---|---|---|
| 50 gal (190 L) | 25 gal (95 L) media | 5–8 fish | 10–20 plants |
| 100 gal (380 L) | 50 gal (190 L) media | 10–15 fish | 20–40 plants |
| 275 gal (1,040 L) | 150 gal (570 L) media | 25–40 fish | 50–100 plants |
| 500 gal (1,900 L) | 250 gal (950 L) media | 50–75 fish | 100–200 plants |
Best Plants for Aquaponics:
- Easy (low nutrient): Lettuce, herbs (basil, mint), bok choy, Swiss chard, watercress
- Medium: Tomatoes, peppers, cucumbers, beans, peas
- Advanced (high nutrient): Melons, squash, large fruiting plants
Start with leafy greens until your system matures (3–6 months), then graduate to fruiting plants as nutrient levels stabilize.
The Nitrogen Cycle: Fish produce ammonia (NH3) through their gills and waste. Beneficial bacteria (Nitrosomonas) convert ammonia to nitrite (NO2), then other bacteria (Nitrobacter) convert nitrite to nitrate (NO3), which plants absorb as fertilizer. This nitrogen cycle takes 4–6 weeks to establish in a new system — called “cycling.”
Water Quality Parameters:
| Parameter | Ideal Range |
|---|---|
| Ammonia (NH3) | 0 ppm (toxic above 1 ppm) |
| Nitrite (NO2) | 0 ppm (toxic above 1 ppm) |
| Nitrate (NO3) | 20–80 ppm |
| pH | 6.8–7.2 (compromise between fish and plants) |
| Dissolved oxygen | 5+ mg/L |
| Temperature | Species dependent |
System Sizing Rule of Thumb: For a 1:1 ratio system (equal volume fish tank to grow bed), you need approximately 4–8 square feet (0.4–0.75 m²) of growing space per adult fish (tilapia-sized). A family of four can be substantially supplied with fresh produce from a 300-gallon (1,135 L) system with 40–50 tilapia and 150 sq ft (14 m²) of growing area.
Common Mistakes: Overstocking fish, underfeeding or overfeeding, neglecting to test water, adding fish before the nitrogen cycle is established, and insufficient aeration. Test water at least weekly and maintain a log of readings.