How many fish in a 20 gallon tank?
A 20 US gal (76 L) tank is usually 24 in (61 cm) long. By size, 23 of the 53 species in this reference fit it. The table shows how many of each the tank can carry if kept on their own, at under 80% of its bioload.
A mix shares the same capacity, so three species at a third each is the limit, not three full rows. Check a mix with the planner; it also weighs water and temperament.
Species that fit a 20 gallon tank
| Species | Adult size | Up to, kept alone | Group |
|---|---|---|---|
| Cardinal tetra | 1.4 in (3.5 cm) | 27 | 10+ |
| Ember tetra | 0.8 in (2 cm) | 43 | 10+ |
| Glowlight tetra | 1.6 in (4 cm) | 23 | 6+ |
| Neon tetra | 1.2 in (3 cm) | 32 | 10+ |
| Endler's livebearer | 1 in (2.5 cm) | 37 | |
| Guppy | 2.4 in (6 cm) | 12 | |
| Platy | 2 in (5 cm) | 14 | |
| Celestial pearl danio | 0.8 in (2.1 cm) | 44 | |
| Chili rasbora | 1.4 in (3.5 cm) | 31 | 10+ |
| Harlequin rasbora | 2 in (5 cm) | 17 | 10+ |
| White cloud mountain minnow | 1.6 in (4 cm) | 27 | 10+ |
| Cherry barb | 2 in (5 cm) | 17 | 10+ |
| Otocinclus | 2 in (5 cm) | 17 | 6+ |
| Pygmy corydoras | 1.2 in (3 cm) | 32 | 6+ |
| Kuhli loach | 4.7 in (12 cm) | 8 | 6+ |
| Betta | 2.8 in (7 cm) | 9 | |
| Dwarf gourami | 3.7 in (9.5 cm) | 4 | |
| Cockatoo dwarf cichlid | 3 in (7.5 cm) | 7 | |
| German blue ram | 1.7 in (4.2 cm) | 19 | |
| Kribensis | 4.3 in (11 cm) | 3 | |
| Cherry shrimp | 1.6 in (4 cm) | 34 | |
| Mystery snail | 2 in (5 cm) | 17 | |
| Nerite snail | 1.5 in (3.8 cm) | 26 |
Fit by size, but not in a full group
- Honey gouramiNeeds a group of 6; the tank carries 2.
Too big for a 20 gallon tank
- Black neon tetraNeeds 72 L (19 US gal), at least 80 cm (31 in) long.
- Black skirt tetraNeeds 68 L (18 US gal), at least 75 cm (30 in) long.
- Congo tetraNeeds 108 L (29 US gal), at least 120 cm (47 in) long.
- Lemon tetraNeeds 72 L (19 US gal), at least 80 cm (31 in) long.
- Rummy-nose tetraNeeds at least 90 cm (35 in) long.
- Serpae tetraNeeds 72 L (19 US gal), at least 80 cm (31 in) long.
- MollyNeeds 81 L (21 US gal), at least 90 cm (35 in) long.
- SwordtailNeeds 108 L (29 US gal), at least 120 cm (47 in) long.
- Zebra danioNeeds 81 L (21 US gal), at least 90 cm (35 in) long.
- Rosy barbNeeds 90 L (24 US gal), at least 100 cm (39 in) long.
- Tiger barbNeeds 72 L (19 US gal), at least 80 cm (31 in) long.
- Bristlenose plecoNeeds 110 L (29 US gal), at least 60 cm (24 in) long.
- Bronze corydorasNeeds 114 L (30 US gal), at least 80 cm (31 in) long.
- Common plecoNeeds 284 L (75 US gal), and grows to 58 cm (23 in).
- Glass catfishNeeds 81 L (21 US gal), at least 90 cm (35 in) long.
- Panda corydorasNeeds 114 L (30 US gal), at least 45 cm (18 in) long.
- Peppered corydorasNeeds 114 L (30 US gal), at least 61 cm (24 in) long.
- Clown loachNeeds 648 L (171 US gal), at least 180 cm (71 in) long, and grows to 40 cm (16 in).
- Yoyo loachNeeds 243 L (64 US gal), at least 120 cm (47 in) long, and grows to 16 cm (6.3 in).
- Paradise fishNeeds 72 L (19 US gal), at least 80 cm (31 in) long.
- Pearl gouramiNeeds 81 L (21 US gal), at least 90 cm (35 in) long.
- AngelfishNeeds 208 L (55 US gal), at least 100 cm (39 in) long.
- Convict cichlidNeeds at least 90 cm (35 in) long.
- DiscusNeeds 255 L (67 US gal), at least 120 cm (47 in) long.
- OscarNeeds 540 L (143 US gal), at least 150 cm (59 in) long, and grows to 46 cm (18 in).
- Boeseman's rainbowfishNeeds 108 L (29 US gal), at least 120 cm (47 in) long.
- GoldfishNeeds 76 L (20 US gal), and grows to 48 cm (19 in).
- Red tail sharkNeeds 243 L (64 US gal), at least 120 cm (47 in) long.
- Siamese algae eaterNeeds 208 L (55 US gal), and grows to 16 cm (6.3 in).
A guide, not a guarantee. Tank sizes: 5 gal, 10 gal, 29 gal, 40 gal, 55 gal, 75 gal, 125 gal.