The AquaGauge Dataset: 2026 Aquarium Stocking Stats
The AquaGauge Dataset shows how densely real keepers actually stock their tanks: corydoras run about 0.2 fish per gallon, shrimp 0.5, guppies and neon tetras about 0.3. Computed from 525 real tanks that reported both a species and a headcount — real stocking density runs lighter than the one-inch-per-gallon rule assumes.
Key stocking statistics (July 2026)
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- Real per-gallon stocking runs about 0.2 corydoras per gallon (median, across 173 sized tanks in the AquaGauge dataset, July 2026).
- Shrimp pack in densest, about 0.5 per gallon (median, across 68 sized tanks in the AquaGauge dataset, July 2026); their bioload is tiny, so colonies scale far past fish rules.
- Guppies and neon tetras run about 0.3 per gallon (median, across 31 and 36 sized tanks respectively in the AquaGauge dataset, July 2026).
- In the popular 11-to-20-gallon range, keepers run a median of 5 corydoras (across 71 sized tanks in the AquaGauge dataset, July 2026), matching the “groups of 6+” guidance.
- The median home aquarium is 20 gallons (across 5,134 real tanks in the AquaGauge dataset, July 2026), the tank most of this stocking happens in.
Real stocking is lighter, and varies by animal
Stocking is where advice and reality diverge most. Real placements in the AquaGauge dataset (July 2026), drawn from tanks that stated both a species and a headcount, run lighter than the one-inch-per-gallon rule assumes, and they vary by animal far more than any single rule captures.
| Species | Median per gallon | Sized tanks (n) |
|---|---|---|
| Shrimp | 0.5 | 68 |
| Corydoras (pygmy) | 0.4 | 22 |
| Guppy | 0.3 | 31 |
| Neon tetra | 0.3 | 36 |
| Corydoras | 0.2 | 173 |
| Otocinclus | 0.14 | 27 |
The spread is the point: shrimp stock roughly 6x denser per gallon than a corydoras, because bioload, not length, is what a tank has to process. A rule that treats an inch of shrimp and an inch of cory the same is wrong in both directions.
What it looks like in a real tank
Translate the per-gallon rates into whole animals and they line up with good care advice, not against it. In the popular 11-to-20-gallon range, the median corydoras tank holds 5 fish (across 71 sized tanks in the AquaGauge dataset), enough for the group of six-plus corydoras need, in the tank size most people own. The median home aquarium across the whole dataset is 20 gallons (n=5,134), so most stocking decisions are being made in a 10 or a 20, not the oversized “starter” tanks advice threads recommend.
The takeaway for a new keeper: real stocking is lighter, per gallon, than beginners fear, and the right number depends on the animal. Size your own tank with the stocking calculator, which models bioload directly, rather than a blanket ratio.
How to cite this page
Cite these figures as: “AquaGauge Aquarium Stocking Statistics 2026, theaquagauge.com/aquarium-stocking-statistics/ (July 2026 snapshot).” The aggregate statistics are licensed CC BY 4.0: use them freely, with attribution; a link back is appreciated. Download the full dataset from the Aquarium Statistics pillar.
Methodology
These numbers are computed directly from the AquaGauge real-tank dataset. Per-gallon rates come from the tanks that stated both a species and a headcount, so each species carries its own sample size (173 corydoras tanks, 68 shrimp, 36 neon tetra). Small samples move medians, so treat the smaller-n species as directional. This page is maintained by Yevhen Bulhakov, editor of AquaGauge. Read more about how we collect the data, or see the full Aquarium Statistics pillar.
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Stocking — under 85% comfortable · 85–100% full · over 100% overstocked
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FAQ
- How many fish per gallon do people actually keep?
- It varies far more by animal than any single rule captures. In the AquaGauge dataset (July 2026), real per-gallon stocking runs about 0.2 corydoras, 0.5 shrimp, and 0.3 guppies or neon tetras per gallon — lighter than the old one-inch-per-gallon rule assumes.
- Is the one-inch-per-gallon rule accurate?
- No. Real stocking in the AquaGauge dataset varies by animal by roughly 5x per gallon (shrimp pack in far denser than angelfish), which no single length-based rule captures. Stock by bioload and adult size, not inches per gallon.
- How many corydoras do people keep in a 20-gallon tank?
- Across 71 real corydoras tanks of 11 to 20 gallons in the AquaGauge dataset (July 2026), the median is 5 corydoras — in line with the 'keep them in groups of 6 or more' guidance, and well short of what an inch-per-gallon rule would allow.
Freshwater aquarist of 8+ years.