How many fish in a 20 gallon tank?
Around 15 small fish in a mix, such as 10 neon tetras and 6 corydoras.
A 20 gallon long is 30 inches by 12, which gives schooling fish real room to swim. A 20 gallon high holds the same water in less floor space.
Stockings that work in a 20 gallon long tank
Each mix has been run through the stocking calculator and comes out with no problems or warnings.
- Neon tetras and panda corydoras95% stocked
10 × Neon tetra, 6 × Panda cory.
- A betta with a school of harlequin rasboras68% stocked
1 × Betta, 8 × Harlequin rasbora.
- A school of zebra danios63% stocked
8 × Zebra danio. This tank is under the recommended minimum for Zebra danio (a 35 x 12 in footprint).
- Cherry barbs and panda corydoras95% stocked
6 × Cherry barb, 6 × Panda cory.
If it is a 20 gallon high
The same water, but 24 x 12 inches on the floor, so less swimming room.
- Neon tetras and panda corydoras89% stocked
10 × Neon tetra, 6 × Panda cory.
- Ember tetras and pygmy corydoras56% stocked
10 × Ember tetra, 6 × Pygmy cory.
Why not one inch of fish per gallon
That old rule says to allow one inch of adult fish per gallon. It is easy to remember and works well for small, slim fish like tetras and rasboras.
It breaks down for bigger and messier fish. A fish twice as long weighs several times as much, and goldfish and plecos make far more waste than their length suggests. Our calculator keeps the inch rule for fish under three inches and counts larger fish for more.
The two kinds of 20 gallon tank hold the same water but not the same fish. Check which one you have before you buy.
One kind of fish, nothing else
The most of each that suits a 20 gallon long on its own.
| Betta | 1 only |
|---|---|
| Neon tetra | up to 21 |
| Ember tetra | up to 31 |
| Guppy | up to 10 |
| Harlequin rasbora | up to 14 |
| Zebra danio | up to 12 |
| Cherry barb | up to 12 |
| Panda cory | up to 12 |
Before you add the last fish
- Add fish slowly. A new tank needs weeks to grow the bacteria that process waste, so add a few fish at a time.
- Count the minimum group. Schooling fish are stressed alone, so plan around the smallest group before the tank total.
- Plan for adult size. Fish in the shop are usually young.
- Match the filter. Look for one rated for 80 to 120 gallons per hour.
A full tank is not a target. One at 60 to 80% is easier to keep clean and gives fish room to settle.
Sizes and weight: 20 gallon long tank dimensions.
Gear for a 20 gallon long tank
Searches on Amazon for the right size. Check the tank size or flow rating on the listing before you buy.
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