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Aquaponics · Calculator

System sizing

Fish tank to grow bed ratio, pump capacity, feed rate, sump volume. UVI-style sizing from any starting point.

System sizing Inputs in L, cm
Just the fish tank, not total system volume. Sump and grow bed water are derived.
Media beds absorb the most feed per square metre, so they need the least bed per fish; rafts need about a third more bed, NFT twice as much.
Standard media bed depth is 30 cm. Rafts are shallower (~20 cm); NFT channels are ~10 cm.
Max fish weight at harvest -- kg total
Grow bed area -- m² of grow bed
Grow bed volume -- L of grow bed water
Minimum pump flow -- L/hr (1× turnover)
Sump volume target -- L of sump
Daily fish feed -- grams of feed per day
Notes --
Numbers assume a cycled, established system feeding warm-water fish at typical rates. Start at 25% of calculated capacity for the first 6-8 weeks while biofiltration builds up.

What this does

Enter a fish tank volume and the calculator estimates the rest of the system: maximum fish weight at harvest, grow bed size, minimum pump flow, sump volume, and daily feed amount. The numbers come from the University of the Virgin Islands aquaponics ratios, which are still the most-cited reference for hobby and small-commercial sizing.

What the ratios mean

Fish density. A hobby system runs 15-40 g of fish per liter of fish-tank water. The old rule of a pound of fish per five gallons is 24 g/L. 40 g/L is tilapia with strong aeration, redundant biofiltration and daily testing; most other species top out lower (the profiles list a maximum per species). 15 g/L gives margin for the inevitable bad day, and it's where I'd start.

Feed rate. A media bed absorbs about 60 grams of fish feed per square meter per day, a raft about 45, an NFT channel about 30, and that feed is what carries the nitrogen the plants need. This is the actual bottleneck of an aquaponics system. Fish density and grow-bed size are derived from how much you can sustainably feed.

Bed-to-tank ratio. For media beds, grow bed volume should equal or exceed fish tank volume. Rafts and NFT have less biofilter surface, so they need more bed area for the same feed, not less.

Turnover. Total system water should pass through the grow beds at least once per hour, ideally twice. Slower turnover means waste accumulates in the fish tank; faster turnover means more pumping cost.

Sump. A sump roughly 25% of total system volume gives flow stability, dampens water-level swings, and provides somewhere to put heaters and air stones out of sight.

Caveats

These ratios assume you've cycled the system and have established biofiltration. A new system can't support its theoretical maximum stocking until the bacteria colony has caught up, which takes 4-8 weeks. Start at 25% of calculated capacity for the first two months and watch ammonia.

The math also assumes warm-water fish (tilapia, perch, catfish) feeding at typical rates. Coldwater fish (trout) eat less per unit weight; calculated grow-bed area will be oversized but the fish stocking is still right.

Pump flow targets are minimums. Larger pumps with throttling valves are usually a better choice than minimum-spec pumps, since flow inevitably drops as biofilms accumulate.

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Further reading