How many fish in a 20 gallon tank?
The standard (high) 20 gallon is 24 in long. If you can, choose the 20 gallon long instead: same water, 6 more inches of swimming room.
A 20 gallon tank (76 L) can hold roughly 33 small fish like neon tetras on their own, or a smaller mixed community. Big fish count for much more than small ones, so plan by adult size and waste, not inches per gallon.
20 gallon stocking ideas
Each plan is checked by our calculator for space, water and compatibility. Add fish gradually to a cycled tank.
Livebearer tank
- 5 × Platies
- 6 × Bronze corydoras
- 2 × Nerite snails
Keep more females than males.
Equipment for a 20 gallon tank
Sized for a 20 gallon tank (24 × 12 × 16 in) with tropical community fish. Your fish may need extras: the stocking calculator builds a list for your exact plan.
- 20 gallon aquarium (tank or kit) (opens Amazon in a new tab)Bigger tanks are more stable and easier for beginners. How to choose
- Aquarium stand for 20 gallons (opens Amazon in a new tab)The water alone weighs about 167 lb (76 kg), before glass, gravel and rock. How to choose
- Adjustable heater, 75 W (opens Amazon in a new tab)Holds about 78 °F (25.5 °C) in a room at 65 °F (18 °C). How to choose
- Aquarium thermometer (opens Amazon in a new tab)Check it daily: heaters can fail stuck on or off. How to choose
- Hang-on-back filter rated 80–120 GPH (opens Amazon in a new tab)Community tank: 4–6 times the tank volume per hour. How to choose
- About 35 lb of aquarium gravel (opens Amazon in a new tab)Enough for a layer about 2 in (5 cm) deep. Smooth gravel suits most community fish. How to choose
- Water conditioner (dechlorinator) (opens Amazon in a new tab)Removes chlorine and chloramine from tap water. Seachem Prime is a popular, concentrated choice. How to choose
- Liquid test kit (ammonia, nitrite, nitrate, pH) (opens Amazon in a new tab)Liquid kits are more accurate than strips. The API Freshwater Master Test Kit is the common choice. How to choose
- Gravel vacuum (siphon) (opens Amazon in a new tab)Cleans the gravel and does the water change in one go. How to choose
- LED aquarium light, about 24 in long (opens Amazon in a new tab)Match the light to the tank length. Basic LEDs grow easy plants. How to choose
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Fish that suit a 20 gallon tank
The number is the most you could keep of that species alone, by bioload. Mix species and you'll need fewer of each.
| Species | Adult size | Keep |
|---|---|---|
| Betta fish | 6.5 cm (2.6 in) | 1 male |
| Bristlenose pleco | 12 cm (4.7 in) | 1 male |
| Dwarf gourami | 7.5 cm (3 in) | 1 male |
| Fancy goldfish | 15 cm (5.9 in) | 1 |
| Guppy | 5 cm (2 in) | 3–19 |
| Neon tetra | 3.5 cm (1.4 in) | 8–33 |
| Panda corydoras | 4.5 cm (1.8 in) | 6–22 |
| Cardinal tetra | 4 cm (1.6 in) | 8–27 |
| Celestial pearl danio | 2.5 cm (1 in) | 8–55 |
| Cherry barb | 5 cm (2 in) | 6–19 |
| Chili rasbora | 2 cm (0.8 in) | 10–77 |
| Ember tetra | 2 cm (0.8 in) | 8–77 |
| German blue ram | 6 cm (2.4 in) | 1 or a pair |
| Glowlight tetra | 4 cm (1.6 in) | 6–27 |
| Harlequin rasbora | 4.5 cm (1.8 in) | 8–22 |
| Honey gourami | 5 cm (2 in) | 1 male |
| Julii corydoras | 5.5 cm (2.2 in) | 6–16 |
| Kuhli loach | 9 cm (3.5 in) | 6–13 |
| Otocinclus | 4 cm (1.6 in) | 6–27 |
| Pea puffer | 2.5 cm (1 in) | 1 male + 2 or more females |
| Peppered corydoras | 6.5 cm (2.6 in) | 6–13 |
| Platy | 6 cm (2.4 in) | 3–14 |
| Pygmy corydoras | 2.5 cm (1 in) | 10–55 |
| Sterbai corydoras | 6.5 cm (2.6 in) | 6–13 |
| White cloud mountain minnow | 4 cm (1.6 in) | 6–27 |
| X-ray tetra | 4.5 cm (1.8 in) | 6–22 |
| Agassiz's dwarf cichlid | 7 cm (2.8 in) | 1 male + 2 or more females |
| Bloodfin tetra | 5 cm (2 in) | 6–19 |
| Bumblebee catfish | 7.5 cm (3 in) | 1–8 |
| Clown killifish | 3.5 cm (1.4 in) | 6–33 |
| Clown pleco | 9 cm (3.5 in) | 1 male |
| Cockatoo cichlid | 7.5 cm (3 in) | 1 male + 2 or more females |
| Endler's livebearer | 3 cm (1.2 in) | 3–41 |
| Forktail blue-eye | 5 cm (2 in) | 8–19 |
| Gardneri killifish | 6 cm (2.4 in) | 1 male + 2 or more females |
| Head and tail light tetra | 4.5 cm (1.8 in) | 6–22 |
| Kubotai rasbora | 2 cm (0.8 in) | 10–77 |
| Lambchop rasbora | 3.5 cm (1.4 in) | 8–33 |
| Peacock gudgeon | 6 cm (2.4 in) | 2–14 (few males) |
| Penguin tetra | 5 cm (2 in) | 6–19 |
| Rosy loach | 2.5 cm (1 in) | 8–55 |
| Rosy tetra | 4 cm (1.6 in) | 6–27 |
| Scarlet badis | 2 cm (0.8 in) | 1 male + 2 or more females |
| Shell dweller cichlid | 4 cm (1.6 in) | 2–27 (few males) |
| Sparkling gourami | 3.8 cm (1.5 in) | 2–24 |
| Threadfin rainbowfish | 4 cm (1.6 in) | 6–27 |
| Zebra pleco | 8 cm (3.1 in) | 1 male |
| Dwarf rasbora | 2.5 cm (1 in) | 10–55 |
| Flame tetra | 3 cm (1.2 in) | 8–41 |
| Green neon tetra | 2.5 cm (1 in) | 10–55 |
| Least killifish | 2.5 cm (1 in) | 6–55 |
| Silvertip tetra | 4.5 cm (1.8 in) | 8–22 |
| Variatus platy | 6 cm (2.4 in) | 3–14 |
Shrimp, snails and other invertebrates
Cherry shrimp, Nerite snail, African dwarf frog, Amano shrimp, Assassin snail, Ghost shrimp, Malaysian trumpet snail, Mystery snail, Ramshorn snail, Bamboo shrimp, Crystal red shrimp, Dwarf orange crayfish, Thai micro crab, Vampire shrimp.
Fish that need a bigger tank
- Angelfish: at least 29 gallons (110 L)
- Common goldfish: at least 75 gallons (284 L)
- Common pleco: at least 150 gallons (568 L)
- Oscar: at least 75 gallons (284 L)
- Tiger barb: at least 29 gallons (110 L)
- Bala shark: at least 230 gallons (871 L)
- Blood parrot cichlid: at least 55 gallons (208 L)
- Boesemani rainbowfish: at least 29 gallons (110 L)
- Chinese algae eater: at least 80 gallons (303 L)
- Clown loach: at least 180 gallons (681 L)
Frequently asked questions
How many fish can go in a 20 gallon tank?
A 20 gallon tank (76 L) can hold roughly 33 small fish like neon tetras on their own, or a smaller mixed community. Big fish count for much more than small ones, so plan by adult size and waste, not inches per gallon.
What are the best fish for a 20 gallon tank?
Good choices include betta fish, bristlenose pleco, dwarf gourami, fancy goldfish, guppy and neon tetra. Pick one centerpiece or one school plus a few bottom dwellers, then check the mix in our stocking calculator.
How big is a 20 gallon tank?
A standard 20 gallon tank is about 24 × 12 × 16 inches (61 × 30 × 41 cm). Full of water it weighs at least 167 lb (76 kg) before glass, gravel and decor.
What fish should not go in a 20 gallon tank?
Angelfish, common goldfish, common plecos, oscars and tiger barbs need more room. For example, angelfish need at least 29 gallons (110 L).
What size heater do I need for a 20 gallon tank?
About 75 W keeps a 20 gallon tank at 78 °F (25.5 °C) in a room at 65 °F (18 °C). Use a bigger heater for a colder room, or check yours with our heater size calculator.
What size filter do I need for a 20 gallon tank?
Choose a filter rated about 80–120 gallons per hour (GPH), which is 4–6 times the tank volume for a typical community tank. Messy fish like goldfish need more; bettas need gentle flow.