Best fish for a 20 gallon tank (and how many)

Best fish for a 20 gallon tank

In order of how well they suit a 20 gallon tank. "Up to" is the most of that one species the tank holds on its own; mixing species splits it.

1. 1.Harlequin rasbora Trigonostigma heteromorpha

   1.75" adult · groups of 8+ · 73–81 °F · pH 6–7.5 · up to 11 in a 20 gallon

   A copper-and-black schooler; Seriously Fish says it really should be kept in a group of at least 8–10 and calls a 60 × 30 cm footprint the smallest it considers.^[1]

2. 2.Neon tetra Paracheirodon innesi

   1.5" adult · groups of 8+ · 72–77 °F · pH 6–7 · up to 13 in a 20 gallon

   The 20 long's 30 inches clears Seriously Fish's 60 × 30 cm minimum for a group of 8–10 neons.^[2]

3. 3.Cherry barb Puntius titteya

   2" adult · groups of 6+ · 68–81 °F · pH 6–8 · up to 10 in a 20 gallon

   A peaceful barb; Seriously Fish suggests buying at least 6–10 and a footprint of at least 60 × 30 cm.^[3]

4. 4.Honey gourami Trichogaster chuna

   2" adult · groups of 2+ · 72–81 °F · pH 6–7.5 · up to 6 in a 20 gallon

   A calm, small gourami and the safer centerpiece, given the iridovirus problem in dwarf gouramis.^[4] Seriously Fish says a 60 × 30 cm footprint suits a pair or small group.^[5]

5. 5.Pygmy corydoras Corydoras pygmaeus

   1.2" adult · groups of 8+ · 72–78 °F · pH 6–7.5 · up to 16 in a 20 gallon

   The bottom-dweller that leaves room for a school above it: about an inch long, in groups of at least 6 and preferably 10 or more.^[6]

6. 6.Ember tetra Hyphessobrycon amandae

   0.8" adult · groups of 8+ · 72–82 °F · pH 5.5–7 · up to 24 in a 20 gallon

   A nano tetra that leaves budget for a second species; Seriously Fish suggests buying 8–10.^[7]

7. 7.White cloud mountain minnow Tanichthys albonubes

   1.6" adult · groups of 10+ · 64–72 °F · pH 6–8 · up to 12 in a 20 gallon

   The unheated option. Seriously Fish warns that permanently warm water shortens its life, so keep it only with other cool-water fish, in a group of 10 or more.^[8]

8. 8.Platy Xiphophorus maculatus

   2.5" adult · groups of 3+ · 68–79 °F · pH 7–8.2 · up to 5 in a 20 gallon

   A hard-water livebearer; Seriously Fish gives a 60 × 30 cm footprint and advises more females than males.^[9]

9. 9.Otocinclus catfish Otocinclus spp.

   2" adult · groups of 6+ · 70–79 °F · pH 5.5–7.5 · up to 10 in a 20 gallon

   An algae-grazing catfish for a mature, planted tank only. Seriously Fish warns they can be delicate when first imported and losses are common; aim for at least 6.^[10]

10. 10.German blue ram Mikrogeophagus ramirezi

    2.5" adult · groups of 2+ · 81–86 °F · pH 4–7 · up to 5 in a 20 gallon

    For experienced keepers: a pair needs soft water at 80–86 °F, and Seriously Fish says it isn't recommended for the general community aquarium.^[11]

Shrimp and snails for a 20 gallon tank

Listed separately: the fish bio-load budget below doesn't describe invertebrates, so they aren't counted in it.

• Amano shrimp Caridina multidentata

  A strong algae eater that doesn't need a group, per Aquarium Co-Op; keep a tight lid on the tank.^[12]

• Cherry shrimp Neocaridina davidi

  A 20 gallon is plenty for a colony; start with at least 10.^[13]

• Nerite snail Neritidae (e.g. Vittina natalensis)

  Grazes algae without overrunning the tank.^[14]

• Mystery snail Pomacea diffusa

  Needs hard water, with a pH of at least 7.2 per Aquarium Co-Op.^[15]

How many of each fish fit in a 20 gallon tank

A 20 gallon long (30 × 12 × 12 in) holds about 16 gallons of water once you take off the glass. Our stocking calculator budgets that water by adult size and body shape: about 0.8 gallons per inch of slim fish (tetras, rasboras), 1.2 for medium-bodied fish (guppies, corys) and 2 for heavy, messy fish (goldfish, plecos). That works out to roughly 20 inches of small, slim adult fish in total. It is an upper limit, not a target: filtration, plants, territory and how often you change water all move it.

Stocking ideas for a 20 gallon tank

Stocking plans that fit the tank's bio-load budget, with a temperature and pH range that suits everything in them.

Fish to avoid in a 20 gallon tank

• Zebra danio · needs 30+ gallons, 36 in long

  Seriously Fish says even a small group needs a 90 × 30 cm (36 inch) footprint, longer than a 20 long.^[16]

• Angelfish · needs 75+ gallons, 40 in long, 16 in front to back

  Seriously Fish's smallest tank for angelfish is 100 × 40 × 50 cm; the smallest standard tank that meets it is a 75.^[17]

• Fancy goldfish · needs 40+ gallons, 36 in long

  Grows to around 8 inches with heavy waste; our species data starts fancy goldfish at 40 gallons.

• Common pleco · needs 125+ gallons, 72 in long

  Reaches about 20 inches and, per ScotCat, needs a 6-foot tank or larger.^[18]

20 gallon tank FAQ

How many fish can you put in a 20 gallon tank?

Roughly 20 inches of small, slim adult fish by our bio-load method: for example 8 neon tetras and a pair of honey gouramis, or 8 ember tetras and 8 pygmy corydoras, both with a little room to spare; 8 harlequin rasboras with a pair of honey gouramis use the whole budget. Group size matters as much as the total; most schooling fish here want 8–10.^{[1, 7]}

How many neon tetras can you put in a 20 gallon tank?

Up to about 13 on their own by bio-load, and at least 8–10 so they school, per Seriously Fish.^[2] With a centerpiece, 8 neons and a pair of honey gouramis fit.

Is a 20 long or a 20 high better for fish?

For most fish, the 20 long. Its 30 inch length meets Seriously Fish's 75 × 30 cm minimum for a group of black skirt tetras, which a 20 high's 24 inches doesn't,^[19] and it gives schooling fish more room to swim.

Can I keep cory catfish in a 20 gallon tank?

Pygmy corydoras, yes.^[6] Bronze and peppered corys grow to about 3 inches and need a group of six; Seriously Fish suggests an 80 × 30 cm footprint for bronze corys,^[20] and six of them use more than a 20's bio-load budget, so they suit a 29 gallon or bigger.

Should I put a dwarf gourami in a 20 gallon tank?

It fits, but Seriously Fish reports that dwarf gourami iridovirus is widespread in farmed stock, with as many as 22% of fish from Singapore carrying it, and that the disease is untreatable.^[4] A honey gourami is the safer centerpiece.^[5]

Can black skirt tetras live in a 20 gallon tank?

Seriously Fish says a group fits a 20 long, but that fin-nipping is usually controlled only in a shoal of 12 or more,^[19] and Tropical Fish Hobbyist notes they nip slow or long-finned tankmates.^[21] Twelve use more than a 20's bio-load budget, so they're better in a bigger tank.