Aquaponics Ratio Calculator

The most widely cited guideline from university extension research is a fish stocking density of 0.5 to 1.0 lb of fish per gallon of fish tank water (60 to 120 g/L) for intensive systems with good aeration and filtration. For beginners, 0.5 lb per gallon is safer. The ratio of fish tank to grow bed volume is typically 1:1 to 1:2 (fish tank : grow bed).

The standard formula is based on the daily fish feed rate. Feed fish 1 to 2% of their body weight per day. Each gram of fish feed per day supports approximately 15 to 20 cm2 of plant grow bed area. So, a system feeding 500 g/day supports 7,500 to 10,000 cm2 (0.75 to 1.0 m2) of grow bed. This is the nutrient balance ratio from USDA aquaponics guidance.

Tilapia is the most widely grown fish in aquaponics systems: it is hardy, grows quickly, and tolerates crowding and wide temperature ranges (22 to 32 degrees C optimal). Other common choices include trout (for cold climates, 10 to 18 degrees C), barramundi (subtropical), carp, catfish, and goldfish or koi for ornamental systems where fish are not harvested for food.

Leafy greens (lettuce, spinach, kale, Swiss chard) and herbs (basil, mint, parsley) grow excellently in aquaponics because they have moderate nutrient needs. Fruiting plants (tomatoes, cucumbers, peppers) grow well but require higher fish stocking densities to meet their heavier phosphorus and potassium needs. Root vegetables are generally not suitable for media-based systems.

For a balanced beginner system, stock fish at 0.5 lb per gallon (60 g/L) of tank volume. A 100-gallon tank supports 50 lb of fish at full stocking. Start at 20 to 30% of maximum stocking density and grow fish up over time. Overcrowding causes ammonia spikes that can crash a system before the biofilter establishes.