Aquarium Stocking Calculator
How the numbers work
Each animal contributes adult size × bioload factor to the load, and the total is compared with your tank volume in gallons. Livebearers and cichlids carry a heavier factor than nano tetras of the same length because they eat more and produce more waste. Three rules then run on top of the arithmetic:
- Species minimum. A tank below a species' minimum footprint fails regardless of the percentage — a 5-gallon tank is never right for a bristlenose pleco.
- Group minimum. Schooling species need their full shoal, so the calculator refuses to call two corydoras a valid stocking plan.
- Pair compatibility. Every combination is checked against our rated comparisons and flagged when temperature, pH, size or temperament clash.
Stocking examples by tank size
Starting points, not limits — open any tank size for the full species list.
| Tank | Species that fit | Example community | Filter turnover | Weekly change |
|---|---|---|---|---|
| 5 gal / 19 L | 5 | 8× Chili Rasbora | 25 GPH | 1 gal |
| 10 gal / 38 L | 19 | 8× Celestial Pearl Danio + 1× Dwarf Gourami + 6× Cherry Shrimp | 50 GPH | 2 gal |
| 20 gal / 76 L | 31 | 6× Neon Tetra + 1× Kribensis + 6× Amano Shrimp | 100 GPH | 5 gal |
| 29 gal / 110 L | 33 | 9× Neon Tetra + 1× Bristlenose Pleco + 6× Amano Shrimp | 145 GPH | 7 gal |
| 40 gal / 151 L | 35 | 12× Neon Tetra + 1× Bristlenose Pleco + 6× Amano Shrimp | 200 GPH | 10 gal |
| 55 gal / 208 L | 36 | 12× Neon Tetra + 1× Bristlenose Pleco + 6× Amano Shrimp | 275 GPH | 13 gal |
| 75 gal / 284 L | 36 | 12× Neon Tetra + 1× Bristlenose Pleco + 6× Amano Shrimp | 375 GPH | 18 gal |
| 125 gal / 473 L | 36 | 12× Neon Tetra + 1× Bristlenose Pleco + 6× Amano Shrimp | 625 GPH | 31 gal |
Four mistakes the calculator catches
- Stocking a new tank on day one. Volume means nothing until the filter is cycled; tick the “mature tank” box only when nitrite reads zero.
- Buying juveniles. Every figure here is adult size. That 2-inch pleco is a 5-inch adult.
- Ignoring footprint. Two tanks of the same volume are not equal — schooling fish need length, not height.
- Counting inverts as free. Shrimp and snails are light but not weightless, especially in nano tanks.
Stocking calculator FAQ
Is the one inch per gallon rule reliable?
No. It ignores body mass, waste output and territory. A 3-inch cichlid produces far more waste than three 1-inch tetras, and a 10-inch goldfish is nothing like ten neon tetras. This calculator weights every species by adult size and a bioload factor, then checks it against the species minimum tank, so the answer changes with what you stock.
What stocking percentage is safe?
Below 85% is comfortable for a cycled tank with weekly 25% water changes. Between 85% and 100% you should stop adding fish and move to 30–40% weekly changes. Above 100% you are relying on your filter to hide a problem that shows up as algae, nitrate creep and short lifespans.
Does the calculator account for filtration?
It assumes a filter rated at roughly five times tank volume per hour, which is the figure it reports for your chosen tank. A stronger filter processes waste faster but does not create swimming space, so it never raises the safe stocking ceiling on its own.
Why does it warn me about group sizes?
Schooling species kept in twos or threes stay pale, hide and often die early. Every species carries a minimum group in our database, so the calculator tells you when a tank is technically big enough for the bioload but too small for a healthy shoal.
Can it check whether my species get along?
Yes. Every pair you add is checked against our 630 rated comparisons, and any risky combination is flagged with a link to the full side-by-side. See the compatibility matrix for the complete set.
Can I share or save my plan?
Your stock list is stored in the page address, so the “copy shareable link” button gives you a URL that reopens the exact plan on any device. The plan is also kept in your browser for next time.