Methodology
We show our work. Every calculator exposes its formula, and our “real-tank” figures come from a transparent, documented dataset — not opinion.
Stocking calculator
Each species in our database has a bioload value — a unit of biological waste load per adult fish, tuned against community norms and adult body mass. We sum the bioload of every fish you add and divide by your tank volume in US gallons to produce a stocking % (~100% = fully stocked). We deliberately reject the “1 inch of fish per gallon” rule because it ignores adult size, waste output and swimming space. Filtration % compares your filter’s GPH to a ~4× turnover target. We also flag minimum tank size, schooling minimums, temperament conflicts and non-overlapping temperature ranges.
Volume calculator
Rectangular: length × width × height (inches) ÷ 231 = US gallons. Cylinder: π × radius² × height ÷ 231. Litres = gallons × 3.785. Filled weight ≈ 10 lb per gallon.
Real-tank dataset
Our “based on N real tanks” figures come from a transparent dataset of 6,414 real home aquariums (the 2026-07 snapshot), aggregated from public posts and comments across 12 aquarium communities on Reddit — posts spanning August 2010 through May 2025. For each tank we extract the stated tank size, species and counts, and water-test readings; clean obvious errors; and compute the median of the stated values — always reported with its own sample size (N). These are a real-world sanity range, not a prescription: always confirm requirements for your specific species and water.
What the dataset covers
Not every tank reports every measure, so each statistic is computed only over the tanks that actually stated it. Current coverage and medians:
| Measure | Tanks reporting (N) | Median |
|---|---|---|
| Tank volume | 5,134 | 20 gallons |
| pH | 741 | 7.4 |
| Nitrate (NO₃) | 1,015 | 10 ppm |
| Nitrite (NO₂) | 733 | 0 ppm |
| Ammonia (NH₃/NH₄) | 902 | 0 ppm |
| Temperature | 369 | 78 °F |
| Species + stocking count | 525 | varies by species |
| Total tanks in dataset | 6,414 | — |
Where the data comes from
The 6,414 tanks are drawn from these public aquarium communities (tanks contributed by each):
| Community | Tanks |
|---|---|
| r/Aquariums | 734 |
| r/Corydoras | 676 |
| r/bettafish | 621 |
| r/Goldfish | 559 |
| r/PlantedTank | 536 |
| r/Fishtank | 529 |
| r/shrimptank | 521 |
| r/Cichlid | 515 |
| r/AquariumHelp | 480 |
| r/Aquascape | 440 |
| r/Discus | 395 |
| r/Guppies | 303 |
| Other aquarium subreddits | 105 |
How we build it
- Harvest. Pull public posts and comments from the 12 communities above.
- Extract. Parse each tank's stated volume, species and counts, and water-test readings (pH, ammonia, nitrite, nitrate, temperature).
- Clean. Normalise units (litres → gallons, °C → °F), drop impossible values, and de-duplicate repeat posts of the same tank.
- Compute. Calculate the median, quartiles (middle 50%), and distribution for each measure over only the tanks that reported it — with an open, auditable tool, never estimated from memory.
- One snapshot, site-wide. Every page cites the same dataset snapshot (currently 2026-07, labeled “July 2026” in the text) and is recomputed when the dataset is refreshed, so no two pages ever assert different values for the same statistic. The flagship Aquarium Statistics page is the canonical copy.
How to read these numbers
- Median, not mean. We report the median because a few very large tanks pull the average up and misrepresent the typical setup.
- Each stat has its own N. A measure computed over 741 tanks is not the same sample as one over 5,134 — we always show the N so you can weigh it.
- Mind the selection bias. This is a self-selected sample of people who chose to post, and many posted because something was wrong. The clean medians reflect well-run tanks; the alarming outliers reflect keepers fixing a problem. Both are over-represented relative to the silent middle.
- It's a range, not a rule. Use these figures to sanity-check your setup, then confirm the real requirements for your specific species and source water.
Data is refreshed periodically; the species database and sample sizes are expanding. See the full breakdown on the Aquarium Statistics page. Found an error? Tell us.